My Mach Number will give you your realtime Mach number anywhere in the atmosphere. This app uses your moving GPS location with respect to your altitude to determine your Mach number. The change in the speed of sound with temperature throughout the atmosphere is accounted for using atmospheric functions developed for this purpose.

My Mach Number even works on aircraft; when your phone is in airplane mode, GPS functionality is still available and My Mach Number will function normally. If you have trouble connecting on older airplanes with aluminum skin, try holding your phone close to the window. Aluminum deflects GPS signals and may make it difficult to use the app on older aircraft.

FAQ
Q >> I get the message 'Please close and restart the app.'?
A >> This is normal and is a result of giving permission to use your GPS Location. This should only occur the first time you use the app.
Q >> The app gets stuck on the GPS loading screen when I'm flying.
A >> This is unfortunately due to the GPS signal being deflected by the aluminum skin of older airplane's airframes. It is much easier to connect before taking off when the airplane is still on the ground. Trying to connect at 20,000 feet is difficult.
Q >> Why does this app need my location?
A >> Your location is necessary because this is how the application determines your speed and altitude as you move around. No data is ever collected or sent to anyone; as an added safety measure, each data point is deleted/overwritten with each GPS location update.