Peter,

You are raising several issues. One is that A and B migh contain text.
The formula I suggested does not mind if there is text in either column
(neither C for that matter). It would mind if there is text in column
D, which is the column with the numeric data to be processed
selectively, if I correctly understand your situation.

The harmonic mean will be calculated in exactly the same way, except
that instead of D2:D100 (oops, just spotted a typo in my suggested
formula) you use 1/D2:D100.

SUMPRODUCT is sort of half way between standard and array formulas.
Without CSE it performs what SUM would do WITH CSE. For example, the
suggested formula, as a purely array formula would be implemented as:

=SUM((A2:A100=K1)*(B2:B100=K2)*(C2:C100=K3)*D2:D10 0)/SUM((A2:A100=K1)*(B2:B100=K2)*(C2:C100=K3))

Only now you would use Ctrl+Shift+Enter (CSE).
But it is not necessarily the function of choice for all the
statistical functions.

An alternative would be a dynamic filter, which would produce in a
separate area all the permissible values according to parameters in
cells. Then you could use your statistical functions and chart over the
dynamic data set.

Write back if your wavelength is in any way along the lines of my post.

Regards,

Kostis