This routine will find the width in pixels of any TI-BASIC screen, if it is written on the graphscreen in small variable-width font. For example, it would return 1 for a single space, 14 for the "cos(" token, and 18 for "Hello". Since it does not actually draw the string, it accepts arbitrarily-long strings, including those wider than 96 pixels.
The width in pixels of "STRING" is returned in Ans from this routine, and can be used as Ans or stored in a variable.
PROGRAM:SUM0TEST :Input "STRING:",Str1 :Disp "WIDTH:",sum(0,Str1