I used to have a 8.5 x 11” transparency that I printed from the web. One can buy it as well in clear plastic.
It had various typesetting "tools" on it. For instance it had a sets of short horizontal lines, each set of which depicted a leading size:
10 points [just improvising here]
You could overlay printed text with these various sizes until one matched, telling you the number of points of leading in that text.
It had other devices as well.
I cannot find the name of this overlay tool.
Any help would be most appreciated.
Best regards to all,