Most .air file record 430 settings I've seen have no drag from M0.0 to M0.6 increasing a little bit from M0.6 to M0.8 then heaps at M1.0.
The pilot's training manual I have says that if you double an aircraft's speed you get 4 times the drag, three times the speed 9 times the drag, four times the speed 16 times the drag, and five times the speed 25 times the drag.
M0.4 is double M0.2, M0.6 three times M0.2, M0.8 four times M0.2, and M1.0 five times M0.2.
The X coordinates in 430 are mach speeds in increments of M0.2 up to M3.2 and the Y coordinates are drag. Only the Y coordinates are editable and this is done using the up/down arrows keys on the keyboard.
As you can only use whole numbers for drag in 430 and you have to start somewhere then,
A. if X=M0.0 Y=0 and X=M0.2 Y=1 then X=M0.4 Y=4, X=M0.6 Y=9, X=M0.8 Y=16 and X=M1.0 Y=25
B. if X=M0.0 Y=0 and X=M0.2 Y=2 then X=M0.4 Y=8, X=M0.6 Y=18, X=M0.8 Y=32 and X=M1.0 Y=50
C. if X=M0.0 Y=0 and X=M0.2 Y=3 then X=M0.4 Y=12, X=M0.6 Y=27, X=M0.8 Y=48 and X=M1.0 Y=75
D. if X=M0.0 Y=0 and X=M0.2 Y=4 then X=M0.4 Y=16, X=M0.6 Y=36, X=M0.8 Y=64 and X=M1.0 Y=100
For subsonic aircraft I use the Y coordinate figure at M1.0 for all Y coordinates above M1.0. In other words the Y coordinates if using A. above would be 0, 1, 4, 9, 16, 25, 25, 25, 25, 25, 25, .......
These 430 settings are directly related to, and may require adjustment of, the Drag Coefficient Zero Lift (parasite Drag) setting in .air file record 1101 or of the parasite_drag_scalar in [flight_tuning] in the aircraft.cfg file.
Starting with set A. then going to set B. if required appears to be a better way of proportionally adjusting drag across the speed range than simply increasing or decreasing the Drag Coefficient Zero Lift in 1101, particularly if there was little or no drag across most of the speed range to begin with (see opening paragraph).
The difference between set A. and set B. above in a DC-3 at 8,000 feet at M0.25 is 2 knots.