Hello Arthur, the graduations are engraved onto a glass plate that is viewed through the knurled eyepiece.
It may be the the glass plate or the viewfinder is dirty, especially if it has been used near cutting fluid.
If it's of interest I can put up a picture of mine.
The company eventually became ;Hilger & Watts', a well known name in optical equipment.
Brian
Edited By Brian H on 02/06/2020 20:16:44
Edited By JasonB on 02/06/2020 20:28:50