Imported by Grandpa from Germany in the 1930's, the paper envelopes are disintegrating, and the instructions are not doing much better;
they spent decades in the hot attic at Steiners Landing in East Rutherford, NJ.
The actual egg tester is in the top right corner of the photo of the instructions, just a small piece of metal on a small string.
(the strings are rotting out also, but you can use a new piece of thread).
You can see Grandpas name and address in the bottom right corner.
This is being sold as an antique or fun item, I do NOT claim that this thing works as advertised.