New Calculator Teacher's Guide This Teacher's Guide presents several classroom activities that make use of Sharp scientific calculators. The purpose of these activities is not to introduce the calculator as a device to relieve the burden of performing difficult calculations, but rather to develop the students' understanding of mathmatical concepts and explore ares of mathmatics that would otherwise be inaccessible. Overhead Calculator for EL-531RH, EL-509RH, EL-531R, EL-509R The OH-509RT calculator features see-through keys and display. By placing the calculator on an overhead projector, students will be able to follow along with the teacher's explanation of key operations or calculations. The OH-509RT can also be used alone. The specifications of the OH-509RT are identical to those of the EL-531RH, EL-509RH, EL-531R and EL-509R.