These gauges are NOT public domain. The files remain copyright by the author ( Trevor de Stigter ) but are supplied as freeware, i.e. they are licensed for use without payment of any fee provided that they are not used in any program or product for which any fee is charged, either directly or indirectly. Where these gauge files are included in any aircraft or panel distribution the foregoing statement must be included in that distribution.
The Engine RPM variables in Flight Simulator 6 (and subsequent) return a value in the range 0-100%. As there is no engine variable to indicate the Max RPM value from the .air file, it is necessary to provide the appropriate scale factor in the programming of each gauge, and then select a gauge with the correct dial scale and the correct 100% RPM value for a particular aircraft.