The "Megger" instrument for measuring the insulation resistance of electrical devices was introduced by the British firm of Evershed and Vignoles in 1905. The name comes from the fact that the insulating resistance of a properly-designed appliance is in the range of tens and hundreds of meghoms. The crank on the end powers a DC generator connected to a specially-designed meter. The instrument, sold in the United States by Biddle of Philadelphia, was presented to the Greenslade Collection by Daniel Chaucer.
 

The Megger is used with "Evershed's Patent Direct Reading Resistance Box" when measuring resistances in the sub-megohm range.