
482 P.2d 302 (1971)
Brian Clark SMITH, Appellant,
v.
STATE of Nevada, Respondent.
No. 6312.
Supreme Court of Nevada.
February 26, 1971.
Alfred Becker, Las Vegas, for appellant.
Robert List, Atty. Gen., Carson City, Roy A. Woofter, Dist. Atty., and Lorin D. Parraguirre, Deputy Dist. Atty., Las Vegas, for respondent.

OPINION
PER CURIAM:
On February 25, 1970 Smith was convicted by a jury of the crime of Possession of a Cheating Device. NRS 465.080. Smith was observed, by a security officer, playing a slot machine in the Thunderbird Hotel in Las Vegas with a twenty-five cent coin having a mono-filament string attached. The device made it possible for Smith to play the slot machine a number of times using only one coin.
Over objection, the security officer was allowed to demonstrate at the trial how the cheating device worked. Smith now contends the trial judge erred by allowing the demonstration without a proper foundation. The security officer testified that the actual slot machine Smith used and the demonstrator were both Bally machines with standard acceptors. *303 He testified both machines were substantially similar. Admissibility of evidence depends upon a foundational showing of substantial similarity between the tests conducted and actual conditions. Ramseyer v. General Motors Corporation, 417 F.2d 859 (8th Cir.1969). The decision whether to allow a demonstration rests largely in the discretion of the trial judge and his decision will not be overturned on appeal absent a clear showing of an abuse of discretion.
Affirmed.
