My first thoughts as to how to approach this problem is to import
excel data.

Here is an example of a similar problem:

I have an excel table with multiples of 10 on the X axis. If the user
inputs an existing X value in the table (10, 20, 30) how do I make a
function return the Y value?

Further, how do I make the procedure 'find' values for non existant X
values? (15, 23, 34) Can I make a function in excel and import it
into vb.net, and have the X values pass through it? Maybe it can
average "between" values?

I hope this is clear, thanks for your time.