Hello smart people

I have a list of survey names in A3:A726 and numbers in M3:M726.
Column M also contains 0 and blanks.

I am doing a summary table on the next sheet so I need a formula to show if
it is 'SurveyName="Manchester" then average 'Autumn 09'!M3:M726 (ignoring
zeros and blanks)

Any help would be greatly appreciated as this is beyond my knowledge.

Many thaks

Paula