190XT Tach With groundspeed

I really like having all the lines on the tachometer with ground speed based on gear. The D21 and D19 tachometers spin the same direction as the 190, and have these marks. Any idea which would have the closest gear ratios?

I don't have a parts/service for either D series to compare transmission specs.

190xt

Gear main counter ratio
1st 36T    13T    0.36
2nd 31T    18T    0.58
3rd 27T    23T    0.85
4th 19T    35T    1.84
Differential 9 to 35 or 3.88
Final drive 13 to 93 or 7.15

I can't figure out the ppower director but I think:

Gear drive driven ratio
Low    27    30    1.11
High   19    26    1.37

'gear' total ratio
1     11.09     
2     13.68
3     17.86
4     22.04
5     26.17
6     32.30
7     56.66
8     69.93


Hmmm. Math isn't adding up. I'm missing something somewhere. But this can start a conversation.

rw wrote: I use an old radar planter monitor that has  ground speed spray...

When I was in the Marines I used to repair the doppler Ground Speed and Drift Angle radar unit that was used on the F4 Phantoms, they weren't much good under 100 Knots or so