Open the program by entering "integ()" into the home screen, or go to "VAR-LINK" (2ND -), highlight "integ" and press "ENTER" then add ")" to it and press "ENTER" again.  

Once in the program, type 1 if an equation is in y1. Then give the lower bound and upper bound and the number of rectangles. (A higher number is more accurate, but takes more time.  

If you get an equation as an answer, then nothing was entered into y1.  

Copyright 2006 Callen Magnuson. All rights reserved.  This program is free to distribute and modify under the GPL license.