Servo altimeter

[Kituu]

I am not able to figure out this question. Please help.

A servo altimeter has a quoted accuracy of 1hPa at MSL. The accuracy in the standard atmosphere is ?

A) +-50ft at 10 000ft and +- 100ft at 40 000ft
B) +-50ft at 20 000ft and +-90ft at the tropopause
C) +-27ft at MSL and +-50ft at 10 000ft

[Alex Whittingham]

As you probably figured out you are being asked how many feet per hPa at different levels. In EASA-land we tend to remember the values for SL, the 500 hPa level and the 200 hPa level which are:

SL 27 ft/hPa
500 hPa (18 000 ft) 50 ft/hPa
200 hPa (39 000 ft) 100 ft/hPa

B looks best to me