:Disp "cranwell@yahoo.com"
:Input "OBJ=?",P
:Input "IMG=?",Q
:Input "FOCAL=?",F
:If F==0:Then
:1/(1/P+1/Q)üZ
:"FOCAL"üN
:Goto Z:End
:If P==0:Then
:1/(1/F-1/Q)üZ
:"OBJ"üN:ZüP
:Goto Z:End
:If Q==0:Then
:1/(1/F-1/P)üZ
:"IMG"üN:ZüQ
:Goto Z:End
:Lbl Z:úQ/PüM
:Disp "",""
:Outpt(7,1,N)
:Outpt(7,7,Z)
:Outpt(8,1,"MAG")
:Outpt(8,6,M)
:Disp ""

    Source: geocities.com/paris/arc/1927/ti85

               ( geocities.com/paris/arc/1927)                   ( geocities.com/paris/arc)                   ( geocities.com/paris)