The fastest car in 1938 had a land speed record of 432km/h. How did they record its speed?

by yesh_me_lorde

You can see it very briefly at around 3 min in this video. https://www.youtube.com/watch?v=DL_mJeb6O04 (I can't name the brand, even though logo is clearly visible; I'm not a car guy)

itty53

FYI that's a Mercedes Benz W125 Rekordwagen. It held the record until this very year, 2017, when Koenigsegg's Agera RS broke it.