"The speed of sound is the rate at which small pressure disturbances will be propagated through the air and this propagation speed is solely a function of air temperature."
Mach# = KTAS/Speed of sound in knots.
Carl remember that when you fly at a "flight level" you are not actually flying at a fixed altitude. Since you are setting 29.92 you are actually changing your altitude above sea level to match the air density of that altitude on a standard day. Temperature and altitude are not directly related however most aircraft charts assume the standard lapse rate (2C/1000').
As for your wiz wheel are you looking at the density altitude or the pressure altitude window for these computations? I found an old wiz wheel to look at and mine actually has a note on it that says, "To obtain TAS from Mach number set true air temp agianst mach number index on "miles" scale read TAS corresponding to mach No. on "minutes" scale." Granted it's TAS but you can work backwards to get your IAS from there. It just shows the correlation between MACH and TEMP.