I am fairly new. I am trying to test if data, text or blank; IF field is text set newfield equal to it; if data, set new field as sum of this field plus another.

Here is what I tried

If(IsValid(S)=0 or S="", S ,T+ S )

assume S is a number fields

If I have an E in Field S it prints out nothing; why? I guess because the E is not valid so it won't print it out

If I had made S a text field it would be valid, but that does not help

if I edit this to read

If(IsValid(S)=0 or S="", "S" ,T+ S )

then it prints out S where relevant; that is because "S" is valid while the field S is not. But that does not help me as I need to print out the text in S

I seem to be in a catch22

I think your problem is that text in a number field is not recognized or stored with the field. The usual idea is to set any field as text that will have text in it. You can then strip out all text with TextToNum() and test whether it equals the original data.