I assume that the blanks are the problem because when you use =VALUE("") you get an error. Try concatenating a zero to the start of SUBSTITUTE so that blanks become zeroes
=SUMPRODUCT(VALUE(0&SUBSTITUTE(A1:A8,"*","")))
or you can use +0 in place of VALUE, i.e.
=SUMPRODUCT((0&SUBSTITUTE(A1:A8,"*",""))+0)
I assume that the blanks are the problem because when you use =VALUE("") you get an error. Try concatenating a zero to the start of SUBSTITUTE so that blanks become zeroes
=SUMPRODUCT(VALUE(0&SUBSTITUTE(A1:A8,"*","")))
or you can use +0 in place of VALUE, i.e.
=SUMPRODUCT((0&SUBSTITUTE(A1:A8,"*",""))+0)
Try
=SUM(VALUE(SUBSTITUTE(A1:A8,"*","")))
and enter it with Ctrl + Shift + Enter, instead of just Enter. This makes it an array formula, and it will treat the A1:A8 range as an array for the SUBSTITUTE() function. Thus, SUBSTITUTE() now evaluates each individual value in A1:A8 separately. VALUE() converts the text to numbers, and sum() adds all of them up.
Edit: The formula =SUMPRODUCT(VALUE(SUBSTITUTE(A1:A8,"*",""))) seems to be working for me. (Normal formula, not an array formula).
Like so?
=SUM(SUBSTITUTE(H3;"μg";"");SUBSTITUTE(J3;"µg";""))
The problem is I want to add values with units in them, without having to do the extra step of creating a separate coloumn where every single value is repeated without the unit just so they can be added up. I thought maybe I could be sneaky and substitute the unit out of the data, add them together and then spit it out. But I guess not. The formula above currently returns the #VALUE! error.