The simple test method using the VISCOSITY COMPARATOR is intended to assess the critical physical property of lubricating and hydraulic oils, i.e. viscosity. The device provides almost immediately and directly on-site the visually observable information whether viscosity of the oil sample is in OK range or not.

I could not find a history or date of first production. Glass is in the case.   It is very vintage and a rare collectable.  Refer to photos for details.