Bf109 test data

[Kodoss]

How is it possible that IAS and TAS are different at 0m altitude? Position error? Why is IAS equal to TAS at 0m altitude for best climb speed?

Since those instruments have springs in it, you can only adjust them perfectly for one messure point (in this case 250 km/h at ground? ). The rest is within a given tolerance.

It is also with old speed-indicators. Their are mostly adjusted to 50 km/h by motorcycles (with top speed below 150 km/h), the rest is tolerated inaccuracy.