Alacrity,
I have a system that uses the BASIC co-processor from FACTS Engineering (not to be confused with Host Engineering). I got it to do complex calculations like computing the time of civil twilight for today. I don't think you'd like the co-processor. It's klunkier than ladder logic. It's like the old service bureau BASIC invented by GE in the 50s or early 60's.
Things I don't like: line numbers, maximum 255 strings all called $, maximum array size 255, variable name rules that make Bakeit and Burnit the same variable, a "glass teletype" user interface that needs a serial cable (can't use the ECOM connection), Line Numbers, odd handling of PLC addresses that are octal (it will accept the value 9 but treat it as 1), odd conversions between binary, hex, octal, bcd, real, ... when communicating with PLC memory, next to worthless error messages, did I mention LINE NUMBERS.
Things I do like: it's always on when the PLC is on, it can access 128 words (which you address in BASIC as 256 bytes) of PLC memory on every scan.
If I had it to do over, I would have thrown away my D2-250-1 and upgraded to a 260. The 260 can do trig.
Roger