The following plots the Mandelbrot set (invented by IBM fellow Benoit B. _) on an HP28S. The required positive integer saved as BntB is the number of iterations that define a point as being in the set. Theory requires _infinity_; I think the _Sci_Amer_ articles used 1,000. I suggest 20->100; plots can take HOURS of continuous computations, and new batteries will probably give you only a few plots. Suggested CntrBBM starting coordinates nicely frame the entire set. You then INS lower left & upper right corners to the stack, ATTN, PMIN & PMAX, et al., and restart with _ALPHA_ _NEXT_ BntB Mndlbrt _ENTER_ or _new_param_ _NEXT_ Mndlbrt. PPAR is automatically recomputed for the minimal 1:1 rectangle which frames & centers your PMIN/PMAX inputs. << DUP TYPE 0 == << ABS IP 'BntB' STO PPAR 2 GET PPAR 1 GET - C->R / 137 32 / / DUP 1 >= << *H >> << INV *W >> IFTE << X PPAR 1 GET IM PPAR 2 GET IM DUP2 SWAP - 31 / PPAR 4 GET * -> cR ym yM yi << ym yM FOR cI cR cI R->C (0,0) 0 -> c z n << DO n 1 + 'n' STO z SQ c + 'z' STO UNTIL n BntB > z ABS 2 > OR END n BntB > << c PIXEL >> IFT >> yi STEP >> PPAR 5 GET IM >> STEP CLLCD DRAW { EQ } PURGE { PMIN PMAX RES CNTR *W *H BntB Mndlbrt } MENU DGTIZ >> IFT >> 'Mndlbrt' STO << { (-6.1015625,-1.25) (4.6015625,1.25) X 1 (9,9) } 'PPAR' STO >> 'CntrBBM' STO * _ALPHA_ CntrBBM 25 Mndlbrt _ENTER_ * _INS_ for diagonal corners, _ATTN_, PMIN/PMAX/RES/CNTR/*W/*H * _ALPHA_ BntB Mndlbrt _ENTER_ ---or,_e.g.--- 40 Mndlbrt Question (I don't have the answer for this, but would like to know): Given that the 28S's mantissa is twelve digits, batteries won't support a BntB much bigger than 100, and letting CntrBBM be "one-power", just HOW much magnification is reasonable? As the math always computes differences from numbers around _1_, it would seem reasonable that you can't go lower than 1E12 mag., but my error analysis isn't that sound.... Feel free to use e-mail, or even AT&T. Glen Kilpatrick (916)756-9321home