This is a bench top Transitestor device for measuring the properties of transistors, diodes and zener diodes. It was made by B.P.L. (Instruments) Ltd and comes from a laboratory. It was working when last used, but I have no way to test it now. It is sold as is.
It is battery powered and the instructions for use are printed on the back of the box for easy reference.
It would be a useful addition to the workbench of vintage radio and electronic hobbyists.