This International Standard defines a system of dimensions for panel mounting of equipment. It is applicable to electrical and electrically operated indicating@ recording and control instruments. It applies to the following types of instruments with protruding bezels: ?C instruments with square housing; ?C instruments with rectangular housing with lateral orientation; ?C instruments with rectangular housing with upright orientation; ?C instruments with round housing and square bezel; ?C instruments with round housing and rectangular bezel. The purpose of this standard is to establish dimensional interchangeability between instruments made by different manufacturers. To fulfil this requirement@ a defined set of dimensions has been chosen. Using these dimensions@ it should be easy to combine instruments of different sizes on the same panel making good use of the available panel space and to produce a satisfactory layout.