Altimeter Errors
I thought that i understood altimeter pressure errors, but i've just come across two different questions on the subject and the answers seem to contradict each other - so basically now i'm confused.
1 - It was my understanding that the ALT was calibrated with respect to ISA pressure lapse rate. When density or pressure are higher the ALT will over read.
However, i've just come across a question. - On leaving an airfield (75ft above MSL) the QNH is set at 1027.5. On approach to the destination airfield (3000ft above MSL) the starting QNH is reset, however the MSL pressure at the destination is 998mb. What will be the error? the answer given is that the ALT will over read by 885ft - hence as pressure decreases ALT will over read.
Can anyone shed any light on this???
Many Thanks