Question: single step debug within a worksheet (or code edit region) "for loop" ?

Hello,

     Can you enter debug in a worksheet vs a proc?   

    I have a for loop that is crashing in the middle with a bad calculated number to provide to a thermoprops function.   Is there a way to single step through a for loop (1500 iterations) to see which line is getting tripped up?  I can not post the worksheet as it's private development.   The question is generic to any "for loop".

   I have also tried "porting" into a code edit region, but still can not enter the debugger mode.   Is proper debugger only available if I turn the "for loop" into a proc?   If yes, what is the availability of packages called right after restart for the worksheet for a proc, or do all the pre-calcs developed in the worksheet and the packages to be variables fed into the proc or packages re-declared insde a new proc ???

  Sorry if this is a trival question.

Thanks in advance,
Bill