How fun - in the "More than one way to deviate a standard" department ...

All 4 of your suggestions worked, although they were all slightly different
from each other.

Teethless mama: =STDEV(IF(D8:AD8=0,D8:AD8))
Bernard: =AVERAGE(IF(ISBLANK(A1:E1),0,A1:E1)) Adjust to taste
Dominic: =STDEV(IF(D8:AD8<"",D8:AD8,0))
T. Valko: =STDEV(D8:AD8+0)

Ain't that a hoot!

Clearly, I need to learn about array formulas - the main thing I was missing.

Thanks all - John D