Thanks again for prompt reply!

But in both cases - TOL=0 and TOL=1 I'm getting incorrect results.

For Y={1,2,3}, X={2,3,5} easily I've got

Sum(Xi^2,i=1..3) = 38

Sum(XiYi,i=1..3) = 23.

Beta=23/38=0.605263158 (exactly as SPSS 17 and Excel's ATP)

(skipped)

SSres=0.078947368

MSE=0.039473684 (exactly as SPSS 17 and Excel's ATP)

For TOL=1: SQRT(MSE / SUM_X^2/(1-0)) = 0.091970901

For TOL=0: can't be calculated

But both SPSS 17 and Excel ATP give me

Beta[1] = 0.605263158 Beta[1] Standard Error 0.032230128