Instrument Comprises of high voltage power supply unit for cathode voltage to CRT ,with intensity, focus, X , Y deflection & solenoid current controls, two analog meters are provided in power supply unit to measure acceleration voltage & solenoid current. Standard Solenoid of multi-turned layers mounted on wooden base. Cathode ray tube mounted to moveable inner side of the standard solenoid. To  determine  the  specific  charge  e/m of  an electron using  Helical Method  (Long Solenoid Method).