Difference between two Average Measure , but exclude if blank

I need to create a measure that I beleived to be simple , 

My measure currently is

AVGVAL_DISP-CALL = [AVG DISP]-[AVG CALL]

That does not work if where the AVG DISP measure has no timestamp in source and results in the CALL Timestamp value being the result and finally the AVG

Is there a way to write a measure that can ignore blanks ?

Do i need to go back to my  source measure that provides me the average ?

AVG CALL = CALCULATE(AVERAGE(frmain[Time]), FILTER(frmain,frmain[Time] <>0))

Thanks for any help