Thanks so much to everyone for the help. On my 86 the line: Y1=A*sin(B*x+C)+D was the one that made it work. Didnt seem to matter if it was upper or lower case. PROGRAM:TRIGFUNC :FnOff :Radian :ZTrig :Disp "Y=Asin(BX + C) + D" :Prompt A,B,C,D :Y1=A*sin(B*x+C)+D :DrawF Y1