As the forecast values are already rounded down, further rounding down increases the error, all be it on the safe side.
I am interested in what CASA would consider the correct answer in an exam. Would they mark you wrong if you used standard mathematical rounding rules, that is .1 to .4 round down, .5 to .9 round up, or would either answer be correct.
The AIP states that the intermediate forecast values are rounded down. I know that observations are rounded down.
Can anyone give an AIP reference that says pilots should always round down when interpolating QNH values?
As I have said, people say that QNH values must always be rounded down. I do not dispute that this is correct, I merely want to read the section in the AIP that makes this statement.
I was simply throwing the question out there for those of said belief, I did not expect to be ridiculed. I was hoping for a reference because it is something that I would like answered properly and conclusively, not because it has any bearing on flight safety but because the requirements need to be clearly defined.
The standard altimeter setting is 1013.2, should anyone dispute that you can have decimals in QNHs.