Originally Posted by snaxmuppet

In one sense you are correct... ground speed does not indicate how fast the aircraft is travelling through the air.

On the other hand, you use the term "indicated airspeed" which is not correct either. As an aircraft climbs into thinner air the air has less effect on the airspeed indicator and so it under-reads... by quite a lot! So the indicated airspeed also won't show the real airspeed either and an adjustment has to be made to allow for the reduced density.

For example... an airliner doing a true airspeed of 500Kts at 38,000ft will likely have an indicated airspeed of around 280Kts!

The Mach meter on the other hand will show the percentage of the speed of sound in the conditions in which the aircraft is flying... the speed of sound depends on the density (and hence temperature) of the air so at sea-level it is about 660Kts and at 35,000 (-55C) it is about 575Kts

Sorry to get technical but it is an interesting topic of Indicated, vs True airspeed vs ground speed vs Mach number.