As an alternative, a device that has not been certified but that has a long record of proven-in-use safe operation may be used in a SIS at the user's discretion. This option requires that the user have detailed failure data for a statistically valid sample of the some model device operating under similar operating conditions. Records must be provided showing the hours of operating usage, the operating environment, the type and frequency of failures. Vendor upgrades to new models may require restarting the time clock on the data.