Abstract: A hand-held instrument for measuring and calculating length, areas, peripheries and volumes is disclosed. The instrument has a housing with a tapered end giving it the overall appearance of a writing instrument. The instrument has a tracking wheel which follows a line or a curve through a revolution of the wheel. The wheel revolutions are then transmitted via an apertured shaft to an opto-electronic device which reads the angular position of the shaft and converts the wheel revolutions into electrical pulses. The pulses are inputed to a calculator which calculates length, surface areas, peripheries and volumes. A display window displays the calculator results. A caster is also disclosed to facilitate measuring curves.