Old instrument box kV 0-25 / R33 porcelain-insulators

A beautiful box mounted in dovetails with a very pretty original mahogany patina and which opens on 2 sides. This case is made for a 2-part measuring instrument. On one side there is a glass and bakelite screen with 0 to 25 kv indication and on the other, 3 insulators (or something that looks like them: -) in porcelain and amber glass. There is a d004c188 mention on the box and a round red stamp with r33. The case is made of wood with black iron handles, some scratches from wear and tear but it is in very good condition. Object of curiosity which attracts attention but which may also interest collectors: -) its dimensions are l 28.5, w 29, h 28.5.