How TT figures pension tax?

We enter info from a 1099-R.  The taxable amount (box 2) is not the same as the gross amount (box 1).  Instead of computing the tax, TT asks how we computed the tax in prior years.  We don't have a clue.  TT has computed the tax for every year for which we have been receiving a pension.  So, TT knows the answer.  In fact we buy TT so that we don't have to know how to figure the tax.  How do we answer the question?  TT wants us to choose between "General rule" and "Simplified method".  We certainly don't know how TT did it last year (or any year).

 

DG