Here's the math...
Okay, here's the math for going both ways with dual tach rings on a watch. The European version of KPH to MPH is probably correct for Europe, as the fastest Grand Prix speed ever achieved is still the legendary Ford GT40, which could do 300 MPH wide open at LeMans.
In the united States, on the other hand, MPH is the standard measure, and in addition they DO get up to 500 MPH on the salt flats of Bonneville, so it would have limited but real utility.
And seeing as I couldn't resist the temptation, I also added a column for an outer tach ring in that most perverted and humorous of all scientific velocity measurements, which is Furlongs (660 feet) per Fortnight (14 days). Obviously, one would need to have THIS tach ring concentric with the week indicator on a perpetual calendar watch. Look for this unique complication on e-Bay or AuthenticWatches.com!!
Tach KPH if MPH if Eqivalent
Ring ring is ring is Furlongs per
Marking MPH KPH Fortnight
60 96.8 37.2 480
65 104.8 40.3 520
70 112.9 43.4 560
75 121.0 46.5 600
80 129.0 49.6 640
90 145.2 55.8 720
100 161.3 62.0 800
110 177.4 68.2 880
120 193.5 74.4 960
130 209.7 80.6 1040
140 225.8 86.8 1120
150 241.9 93.0 1200
160 258.1 99.2 1280
170 274.2 105.4 1360
180 290.3 111.6 1440
190 306.5 117.8 1520
200 322.6 124.0 1600
220 354.8 136.4 1760
240 387.1 148.8 1920
260 419.4 161.2 2080
280 451.6 173.6 2240
300 483.9 186.0 2400
350 564.5 217.0 2800
400 645.2 248.0 3200
450 725.8 279.0 3600
500 806.5 310.0 4000
