Setting conditions for an average field

[#1]

Hi guys,

I'm trying to do an average of a field if a condition is met .

I've tried this but its not working any ideas where im going wrong !

This is the original statement  which works fine :

Avg($(vFactor1))-1/3

I wanted to include something to only do the average where Wave =vWaveCurr

I tried this and it was not working 😕

Avg($(vFactor1) and Wave = vWaveCurr )-1/3

[#2]

Thanks this really helps me is it possibility to have vFactor1 instead of heading 1 as the heading names change quite a lot 

the trouble is I cant change the factor definition as it feeds into other sources

Thanks

Sarah