217 F.3d 905 (7th Cir. 2000)
UNITED STATES OF AMERICA, Plaintiff-Appellee,v.BOB BRUMLEY, Defendant-Appellant.
No. 99-2948
In the  United States Court of Appeals  For the Seventh Circuit
Argued January 20, 2000Decided July 12, 2000

Appeal from the United States District Court for the Southern District of Indiana, Indianapolis Division.  No. 98 CR 146--John D. Tinder, Judge.[Copyrighted Material Omitted]
Before COFFEY, MANION and ROVNER, Circuit Judges.
ROVNER, Circuit Judge.


1
A jury convicted Bob  Brumley of conspiracy to possess with intent to  distribute methamphetamine, in violation of 21  U.S.C. sec. 841(a)(1). Brumley challenges both  his conviction and his sentence on a number of  grounds, contending that his confession was  involuntary, that he was entitled to a new trial  on the basis of newly discovered evidence, that  a DEA agent was erroneously allowed to give  expert testimony, that the indictment was flawed,  and that the disparity between Brumley's sentence  and that of his co-conspirators justified a  downward departure for his sentence. We affirm.

I.

2
In January 1997, Bob Brumley introduced Ralph  Meade to Jack Bishop at a party at Brumley's  home. Later, Brumley asked Meade if he could  supply Brumley with methamphetamine, telling  Meade that Bishop was capable of selling large  quantities of the drug. Meade apparently  responded favorably because Brumley then told  Bishop that Meade could supply unlimited amounts  of methamphetamine. Thereafter, Brumley served as  a middleman between Meade and Bishop. On  approximately six occasions between January 1997  and October 1998, Brumley supplied Meade with  cash and sometimes with rental cars so that Meade  could travel to California to purchase  methamphetamine. When Meade returned to Indiana,  Brumley typically picked the drugs up from  Meade's house and delivered them to Bishop, who  sold the drugs locally. Brumley was a user as  well as a dealer, and accepted both  methamphetamine and cash in payment for his role  in the arrangement. Apparently, he helped himself  to a little too much of the take, and Meade and  Bishop decided to cut him out of the loop when  they discovered he had withheld three pounds of  methamphetamine from Bishop. Meade and Bishop  continued to provide Brumley with drugs to keep  him quiet, but Meade began making deliveries  directly to Bishop. All tolled, Meade transported  approximately 28 pounds of methamphetamine from  California to Indiana, with 20 pounds being  funneled through Brumley and the rest being  delivered directly to Bishop.


3
On Meade's last road trip, a Texas police  officer stopped him for exceeding the posted  speed limit. The officer asked for consent to  search the vehicle, and Meade gave his consent.  The officer found in the car two partially opened  5-gallon detergent buckets, each containing  individually wrapped plastic bags filled with  methamphetamine. Meade was arrested and decided  to cooperate with law enforcement. He identified  his California source, and agreed to make a  controlled delivery to Bishop, but did not  mention Brumley out of friendship. Bishop was  arrested as a result of the controlled delivery  and he also decided to cooperate with law  enforcement. Bishop implicated Brumley and told  the officers that Brumley carried a gun on  occasion when delivering methamphetamine to  Bishop's home. Meade ultimately implicated  Brumley as well, telling the officers that  Brumley acted as a middleman.


4
Shortly after these arrests, DEA agents executed  a search warrant at Brumley's home in Indiana.  The agents recovered methamphetamine, scales,  cash, and two handguns, one in the house and  another in a truck parked in the garage. They  also recovered a slip of paper containing the  phone number of Meade's source in California. The  agents advised Brumley of his Miranda rights, and  Brumley was cooperative throughout the search.  Brumley was arrested and taken to DEA  headquarters. Approximately three and a half  hours after the agents began the search at  Brumley's home, two agents began to interrogate  Brumley. Although Brumley later disputed this  point, the agents testified that they read  Brumley his Miranda rights once again, and that  Brumley then signed the waiver portion of the  Miranda form. Thereafter, Brumley made  inculpatory statements to the agents that were  used against him at trial.


5
In the district court, Brumley moved to  suppress his post-arrest statement on the ground  that he had not knowingly and voluntarily waived  his Miranda rights. The district court held a  hearing and found that the agents read Brumley  his Miranda rights during the search of his house  and later at DEA headquarters. The court also  found that Brumley signed the waiver of rights  form, and had in fact knowingly and voluntarily  waived his Miranda rights. The case proceeded to  trial where the district court allowed a DEA  agent to testify as an expert on the issue of  what quantities of methamphetamine constituted  user and dealer amounts. Brumley objected to this  testimony on the ground that the agent was not  qualified to testify as an expert. After  requiring additional voir dire of the witness,  the district court allowed the agent to testify  as an expert. The jury found Brumley guilty and  the court sentenced him to 151 months of  incarceration. His co-conspirators, who both  cooperated with the government, were sentenced to  considerably shorter terms of 71 months for Meade  and 63 months for Bishop. Brumley appeals.

II.

6
On appeal, Brumley contends that his confession  should have been suppressed at trial because he  did not knowingly and voluntarily waive his  Miranda rights and because his statement was made  in the course of plea negotiations and was  therefore inadmissable under Federal Rule of  Criminal Procedure 11(e)(6)(D). He also objects  to the DEA agent's expert testimony because the  agent's opinion was based on subjective belief  and not on any reliable methodology. Brumley  asserts that the agent's opinion testimony was  highly prejudicial and did not assist the trier  of fact. Finally, Brumley complains that the  district court erred in sentencing him because  his maximum sentence should have been controlled  by 18 U.S.C. sec. 371 due to an ambiguity in the  indictment, and because the district court  refused to recognize that the disparity between  his sentence and that of his co-conspirators was  a valid basis to depart downward.

A.

7
"We review de novo a district court's  determination of whether a Miranda waiver was  knowing and voluntary." United States v.  Schwensow, 151 F.3d 650, 659 (7th Cir. 1998),  cert. denied, 525 U.S. 1059 (1998). We review  findings of historical fact deferentially,  however, and reverse only for clear error. Id.  Brumley complains that the district court erred  in finding that he knowingly and voluntarily  waived his Miranda rights. At the suppression  hearing, Brumley denied that the agents read him  his rights when they executed the search warrant  at his home, and testified that he did not recall  seeing or signing the Miranda waiver form at the  DEA office where he was questioned a few hours  later. The agents, of course, told a different  story and the district court found the agents  more credible.


8
Normally, that observation would end our  inquiry, but here Brumley raises what he  characterizes as a newly discovered fact that he  claims calls the agents' credibility into  question. At the suppression hearing, Brumley  admitted that the signature on the Miranda waiver  appeared to be a copy of his signature (he was  shown a photocopy of the form at the hearing),  but denied having signed the form. After trial,  he requested that the court allow a handwriting  expert to examine the document. Over the  government's objection, the court allowed the  expert to examine the original waiver form.  Brumley's own expert confirmed that the signature  on the form was indeed Brumley's, but the expert  found other marks on the document that could have  been attempts to alter the form. In particular,  there was evidence that someone had changed the  "taken into custody" time on the form, and there  were also ink touch-ups that the expert believed  were an attempt to match ink colors. The expert  also identified indented writing on the face of  the document in three different places, but was  unable to identify what the writing said without  further testing. Brumley moved for further  testing of the document, theorizing that he  signed the document, if at all, as part of a  stack of documents he signed while in court one  day. He also moved for a new trial as a result of  this newly discovered evidence. The district  court denied the motion for further testing, and  also denied the motion for a new trial. Brumley  now argues that the district court abused its  discretion in refusing to allow further testing  of the Miranda form and also erred in refusing  his request for a new trial.


9
The decision whether to grant a new trial is  within the discretion of the district court.  United States v. Gonzalez, 93 F.3d 311, 315 (7th  Cir. 1996). Because he is relying on newly  discovered evidence, Brumley must show that he  became aware of the evidence only after the  trial, that he could not have discovered the  evidence by due diligence any sooner, that the  evidence is material and that the evidence would  probably lead to an acquittal in the event of a  new trial. Id.; United States v. Fruth, 36 F.3d  649, 652 (7th Cir. 1994), cert. denied, 513 U.S.  1180 (1995). Brumley's argument fails on at least  the first two prongs of the test for newly  discovered evidence because Brumley himself  surely knew before trial whether or not he had  knowingly signed a waiver of his Miranda rights.  He knew from the time of the suppression hearing  at the latest that the government intended to  rely on that written waiver. He could have moved  to examine the document before trial but did not  do so. The district court generously allowed him  to examine the form after trial, but the court  was under no obligation to offer even more post-  trial discovery given Brumley's lack of diligence  before trial. Brumley makes no attempt on appeal  to explain this lack of diligence. The court was  within its discretion to deny the motion for a  new trial based on Brumley's lack of diligence in  pursuing this evidentiary lead.


10
Brumley also contends that his confession was  inadmissable because it was made in the course of  plea negotiations. Federal Rule of Criminal  Procedure 11(e)(6)(D) provides that statements  made in the course of plea discussions with an  attorney for the government which do not result  in a plea of guilty or which result in a plea of  guilty later withdrawn are not admissible against  the defendant who participated in the plea  discussions. Brumley did not confess to a  government lawyer; he confessed to DEA agents. He  argues, however, that the agents were acting with  apparent authority for the United States  Attorney's Office when they told Brumley they  would help him if he helped them. Brumley  contends that the agents acted as if they had  authority to control the outcome of the case,  that they offered his wife immunity if she would  cooperate against her husband, and that the  agents acted as if Brumley's cooperation would  lead to a plea agreement disposing of the case.


11
Brumley did not raise this issue before the  district court and therefore must pass the high  hurdle of proving that the district court  committed plain error. United States v. Kincaid,  212 F.3d 1025, 1030-31 (7th Cir. May 16, 2000). A  party must raise and develop an argument before  the district court or in its motions in order to  provide the district court with an opportunity to  consider all matters before it. Id. Because  Brumley deprived the court of this opportunity,  we deem this issue forfeited, and we review only  for plain error. Id. Plain error review allows us  to correct particularly egregious errors for the  purpose of preventing a miscarriage of justice.  Id. Brumley relies on a footnote in an Eighth  Circuit case in support of his claim that Rule  11(e)(6)(D) applies to discussions with DEA  agents as well as discussions with government  attorneys if the agents represent that they are  working on behalf of the United States Attorney's  Office. See United States v. Millard, 139 F.3d  1200, 1205 n.4 (8th Cir. 1998), cert. denied, 525  U.S. 949 (1998). In that case, the agent told the  defendant that he was working directly with a  particular Assistant United States Attorney  ("AUSA"), that he had spoken to the AUSA about  cooperation, and that if the defendant was  interested in cooperating with the government,  "we would offer him a particular deal." Moreover,  while the agent was speaking with the defendant,  he telephoned the AUSA to discuss what kind of  deal could be offered to the defendant. Id.


12
Because Brumley did not raise this issue before  the district court, the court never had an  opportunity to rule on the factual much less the  legal basis for Brumley's claim. We are left with  Brumley's version of what the agents told him.  Even if we take Brumley's version of events as  true, however, we reject this claim for two  reasons. First, Millard is distinguishable. The  agent in that case made affirmative  representations to the defendant that the agent  was working with the AUSA to offer a particular  deal if the defendant cooperated. Here, the  agents made general statements that law  enforcement officers commonly make, that  cooperation would likely lead to a better outcome  for the defendant. These statements were both  true and innocuous. Second, and more importantly,  our case law rejects this kind of argument. We  pointed out in United States v. Springs, 17 F.3d  192, 195 (7th Cir. 1994), cert. denied, 513 U.S.  955 (1994), that the phrase "with an attorney for  the government" was added to Rule 11(e) (6)(D) in  1979 precisely to prevent the argument that a  voluntary statement made to law enforcement is  rendered inadmissable merely because it was made  in the hope of obtaining leniency by a plea. See  also United States v. Lewis, 117 F.3d 980, 984  (7th Cir. 1997), cert. denied, 522 U.S. 1035  (1997) (Rule 11(e)(6) applies only to statements  made to government attorneys and not to  statements made to law enforcement agents). The  agents here did not, even by Brumley's account,  purport to be acting on behalf of the United  States Attorney's Office. There is no reason to  extend Rule 11(e)(6) under these facts, and the  district court did not commit plain error by  failing to suppress Brumley's statements on this basis.

B.

13
Brumley also objected to the admission of DEA  Agent Dan Schmidt's testimony regarding what  amounts of methamphetamine constituted user  quantities and what amounts were dealer  quantities. Specifically, Brumley disputed the  agent's conclusion that any amounts in excess of  one ounce were distribution as opposed to  personal use amounts. Brumley raises four  objections to the admission of this testimony.  First, the agent's opinion was based on his  subjective belief or unsupported speculation.  Second, the agent's opinion was not based on any  professionally sound or reliable underlying  methodology. Third, the agent was merely vouching  for the credibility of one of Brumley's co-  conspirators. Fourth, the agent's opinion  testimony was highly prejudicial but did not  assist the trier of fact in understanding the  evidence or determining a fact in issue.

Federal Rule of Evidence 702 specifies

14
If scientific, technical, or other specialized  knowledge will assist the trier of fact to  understand the evidence or to determine a fact in  issue, a witness qualified as an expert by  knowledge, skill, experience, training, or  education, may testify thereto in the form of an  opinion or otherwise.


15
The government sought to qualify Agent Schmidt as  an expert in the area of drug trafficking,  including packaging quantities, distribution  methods, and user quantities versus distribution  quantities. Agent Schmidt had approximately seven  years of law enforcement experience, much of it  involving investigations relating to narcotics  and other drugs, including methamphetamine. He  had, in the course of those investigations,  interviewed people he arrested who decided to  cooperate with the government. He testified that  through his investigations and experience, he  became familiar with how methamphetamine is  packaged and sold, including prices and  quantities. He testified that as a result of the  approximately one hundred methamphetamine  investigations in which he had participated, he  knew what quantities of methamphetamine were for  personal use and what quantities were dealer  amounts. On the basis of this testimony, the  district court allowed Agent Schmidt to testify  that, in his opinion, an ounce or more of  methamphetamine constituted a dealer quantity.  Because Brumley was charged with possession with  intent to distribute, possession of dealer  quantities was probative as to Brumley's intent,  and the government indeed sought to use this  testimony to prove Brumley's intent to  distribute.


16
The admission of expert testimony from technical  fields is governed by the same concerns and  criteria as the admission of scientific expert  testimony. Walker v. Soo Line Railroad Co., 208  F.3d 581, 590 (7th Cir. 2000). See also Kumho  Tire Co., Ltd. v. Carmichael, 119 S.Ct. 1167,  1174-76 (1999); Daubert v. Merrell Dow  Pharmaceuticals, Inc., 509 U.S. 579, 590 n.8  (1993). We review de novo "whether the district  court properly followed the framework set forth  in Daubert." Walker, 208 F.3d at 590 (citing  United States v. Hall, 165 F.3d 1095, 1101 (7th  Cir. 1999), cert. denied, 527 U.S. 1029 (1999)).  If we determine that the district court properly  applied the Daubert framework, we review the  district court's decision to admit or exclude  expert testimony only for an abuse of discretion.  Walker, 208 F.3d at 590. The Supreme Court in  Kumho Tire explained that the Daubert  "gatekeeper" factors had to be adjusted to fit  the facts of the particular case at issue, with  the goal of testing the reliability of the expert  opinion. 119 S. Ct. at 1175. For example,  engineering testimony rests on scientific  foundations, but "[i]n other cases, the relevant  reliability concerns may focus upon personal  knowledge or experience." Id. The reason for this  needed flexibility is that there are many  different kinds of experts and many different  kinds of expertise, including experts in drug  terminology, handwriting analysis, land  valuation, agricultural practices, railroad  procedures, and so forth. Id.


17
The district court applied this flexible  approach by determining the extent and type of  experience that Agent Schmidt had in the area of  methamphetamine distribution. The court carefully  limited both the questioning and the agent's  testimony to reflect only those areas in which  the agent had extensive experience and training,  and in which the jury would be aided by his  testimony. The district court therefore applied  the Daubert gatekeeping tests for relevance and  reliability and we will review the court's  decision to admit this evidence for abuse of  discretion only. Addressing Brumley's objections  seriatim, the record reveals that the agent's  testimony was based not on his subjective belief  or unsupported speculation but rather on his  extensive experience investigating  methamphetamine distribution crimes. For example,  the agent testified that in his experience,  methamphetamine was sold on the streets of  Indiana during the relevant time frame for $100  per gram, and that there are approximately 28  grams in an ounce. From his experience, the agent  testified that an ounce or more of  methamphetamine constituted a dealer quantity. As  the district court pointed out, another expert  might disagree with this opinion, but the  disagreement does not render the opinion  inadmissable. Rather, Brumley was entitled to  cross-examine Agent Schmidt and to put on his own  expert to offer a counter opinion. That addresses  Brumley's second objection as well, that Agent  Schmidt's opinion was not based on any  professionally sound or reliable underlying  methodology. The opinion was based on his  extensive investigative experience, and Kumho  Tire explains that the reliability of different  kinds of expertise may be shown in different  ways.


18
Nor was the agent merely vouching for the  credibility of Meade, one of Brumley's co-  conspirators who testified that Brumley  participated in the distribution ring. Meade  testified that Brumley once participated in a two  ounce sale of methamphetamine to a third party.  It is difficult to understand how the agent's  testimony that two ounces is a dealer quantity  vouches for the credibility of Meade, and Brumley  does not adequately explain the connection, if  any exists. The agent's testimony merely tended  to prove that if Brumley was in possession of two  ounces of methamphetamine, he was in possession  of a dealer quantity. Meade, on the other hand,  testified that Brumley actually sold the two  ounce quantity to another person. The agent's  testimony was unrelated to Meade's credibility.


19
Finally, Brumley complains that the evidence was  highly prejudicial and did not aid the jury. The  government responds that the evidence was proper  under Federal Rule of Evidence 704(b) because the  agent did not explicitly refer to Brumley's  mental state, and the agent made clear through  his testimony that he did not possess special  knowledge of the defendant's mental process, but  rather was basing the opinion on his expert  knowledge of criminal practices. Rule 704(b)  provides that an expert witness testifying with  respect to the mental state of a defendant in a  criminal case may not state an opinion or  inference as to whether the defendant did or did  not have the mental state constituting an element  of the crime charged because such ultimate issues  are for the trier of fact alone. We addressed a  very similar issue in United States v. Mancillas,  183 F.3d 682 (7th Cir. 1999), cert. denied, 120  S. Ct. 1271 (2000). At the trial in that case,  the government presented a hypothetical to a  testifying DEA agent, regarding a person  possessing a plastic bag containing 400 grams of  marijuana, a slip of paper bearing the notation  "420 g," a handgun, a scale, two pagers, a  cellular phone and $2440 in cash. After setting  forth these hypothetical facts, the government  asked the agent whether, in his opinion, the  marijuana was being held for distribution or  personal consumption. The agent testified that in  his opinion, the marijuana was being held for  distribution. 183 F.3d at 705. We held that such  testimony should not be excluded as long as it is  made clear, either by the court expressly or by  the nature of the examination, that the opinion  is based on the expert's knowledge of common  criminal practices and not on some special  knowledge of the defendant's mental state. Id.


20
Brumley disavows Rule 704(b), stating that his  objection is rather based on the fact that none  of Agent Schmidt's experience or training was  related to distinguishing user quantities from  dealer quantities. However the argument is  framed, the result is the same. The district  court properly determined that Agent Schmidt had  expertise in the matter of distinguishing user  from dealer quantities, expertise gained through  his extensive experience investigating crimes of  this very nature. Brumley's argument goes not to  the admissibility of this evidence but rather to  its weight, and he was free to cross-examine the  agent about the basis for his opinion. Through  cross-examination and testimony from his own  witness, Brumley was free to reveal any  weaknesses or errors in the agent's opinion.  Because the district court carried out the  gatekeeper function appropriately and limited the  evidence to those areas in which the agent had  expertise gained through experience and training,  we affirm the admission of Agent Schmidt's expert  testimony.

C.

21
Brumley asserts two grounds for error in his  sentence. First, he complains that the indictment  did not specify whether he was being charged  under 21 U.S.C. sec. 846, the drug conspiracy  statute, or 18 U.S.C. sec. 371, the general  conspiracy statute. The main difference in proof  between these two statutes is that under sec.  371, the government must prove an overt act in  furtherance of the conspiracy. The indictment,  which did not specify which conspiracy statute  applied, did allege overt acts in furtherance of  the conspiracy. Because of this ambiguity in the  indictment, Brumley contends that he should have  been sentenced under sec. 371, which has a  statutory maximum of 60 months. Section 846, on  the other hand, has a minimum sentence of 120  months, and thus the difference is significant.  Brumley also objects to the district court's  refusal to entertain a downward departure in his  sentence based on the disparity in sentencing  between Brumley and his co-conspirators.


22
An error in the citation of the statute charged  in an indictment is not a ground for reversal  unless the error misled the defendant to the  defendant's prejudice. Federal Rule of Criminal  Procedure 7(c)(3). The district court noted that  Brumley was not misled by the error because he  was informed at his initial hearing before a  magistrate that he faced a possible sentence of  ten years to life, and he also signed two  documents at that time that indicated he was  being charged under sec. 846. At trial, the  government proposed instructions citing sec. 846  and Brumley did not object to these instructions.  Indeed, the first time he brought the error to  the court's attention was after trial. The  district court therefore concluded that Brumley  was not misled by the error. We agree. There was  nothing in the record that would lead us to  believe Brumley was misled about the charges he  faced. Brumley complains that the ambiguity lies  in the general verdict that the jury returned  because the government alleged and proved overt  acts in furtherance of the conspiracy, which is  consistent with sec. 371. Because the elements of  both sec. 371 and sec. 846 were satisfied,  Brumley claims the court should be limited in  sentencing him to the maximum penalty under sec.  371. As the district court noted, the jury was  instructed that they need not find that Brumley  committed any overt acts in order to convict him.  There is thus no ambiguity as to which statute  Brumley was charged with or convicted under, and  any error or omission in the indictment was  harmless.


23
We turn finally to Brumley's claim that the  district court erred in determining that the  disparity between Brumley's sentence and Bishop's  sentence was not a valid basis to depart  downward. Brumley maintains that there is an  unjustified disparity between his sentence and  Bishop's sentence, caused by the government's  conduct at Bishop's sentencing hearing. At  Bishop's detention hearing, the government urged  the court to find that a gun found in Bishop's  possession was a dangerous weapon related to drug  dealing. After Bishop cooperated with the  government, the government urged the court at his  sentencing hearing to find that the gun was not  related to the drug crime but was rather a family  heirloom. As a result of that finding and other  factors relating to Bishop's cooperation, Bishop  received a reduced sentence of 63 months,  considerably shorter than Brumley's 151 month  sentence. At Brumley's sentencing hearing, the  court found that the disparity was justified by  a proper application of the guidelines and  therefore the district court refused to depart  downward.


24
We lack jurisdiction to review a district  court's discretionary refusal to depart downward  unless the sentence was imposed in violation of  the law, or was imposed as the result of an  incorrect application of the guidelines. United  States v. Winters, 117 F.3d 346, 348 (7th Cir.  1997), cert. denied, 522 U.S. 1063 (1998).  Brumley claims the district court made a legal  error in concluding that it could not depart on  the basis of a disparity in sentencing. But the  district court was clearly aware that it could  depart for an unjustified disparity, and found  that the disparity here was justified by the  factual circumstances of this particular case.  Such a discretionary ruling is not reviewable by  this Court. We note that the government cited our  opinion in United States v. McMutuary, 176 F.3d  959 (7th Cir. 1999), without noting that we  vacated that opinion several months before the  government filed its brief. See United States v.  McMutuary, 200 F.3d 499 (7th Cir. 1999). That  oversight does not change the analysis. In our  recently released revised opinion in McMutuary,  we did not change the core holding of United  States v. Meza, 127 F.3d 545 (7th Cir. 1996),  cert. denied, 522 U.S. 1139 (1998), that a  justified disparity can never serve as a basis  for a departure from the Guidelines sentencing  range. See United States v. McMutuary, 217 F.3d 477. 489-90 (7th Cir. June 21, 2000). We went  even further to say that, ordinarily, disparities  between the sentences of co-defendants should not  be considered a factor in the decision to depart  from the Guidelines. Id. Rather, we held, a  sentencing court should consider unjustified  disparities only in those cases where the  disparity exists between the defendant's and all  other similar sentences imposed nationwide. Id.  That seals the case against Brumley, for his  sentence is the result of a straight-forward  application of the Guidelines. Even if he were  able to show that a disparity exists between his  sentence and Bishops's, he cannot, therefore,  show that his sentence is disparate from the  sentences of defendants similarly convicted  throughout the United States.


25
AFFIRMED.

