As a courtesy, Metcalfe Models provides a sheet with OO, HO, and N scale rulers that can be glued to cardstock, or thin styrene, for use when model building on their web site:
https://www.metcalfemodels.com/wp-content/uploads/2017/01/Scale_Rulers.pdf
They are intended for printing on A4 size paper (210×297mm/8.27×11.69in), which is available on Amazon if you can't find it locally. In a pinch you can print them on regular 8.50x11.0in letter size paper. Just be sure your PDF viewer and printer are set to 100%, not "Scale to Fit".
What I like about these is it's very easy to make multiple rulers so you can make measurement notes about specific buildings and structures directly on the ruler itself, e.g., tick marks a certain distance apart with a note "Window spacing" for a factory wall. I have one set I rubber cemented to some old steel rules for drawing straight lines and as cutting guides.
Almost forgot to mention, if you reduce the print size to 73% the HO ruler will become a TT scale (1:120) ruler, and the N ruler will become a Z scale (1:220) ruler. Just be sure to mark them so you know what they are.
I hope you find them useful.
Len
Those are a good idea. It would be a help if they put a regular inch scale along the opposite side of it. Not flip it over, but next to it.
You could always cut the scale rule down so the inch marks of a cheap plastic, or steel, rule are exposed when you glue the scale rule to it. Something like this, available at Wally-Mart and other retailers, should work:
(https://i5.walmartimages.com/asr/bb46ff2c-46cb-44ee-bed2-38ecc84b905c_1.014f78dee5b70e2b3e0ed012bad16189.jpeg?odnHeight=450&odnWidth=450&odnBg=FFFFFF)
You could leave either the inch or metric side exposed, depending on your preference.
Len
Len - That's a really good idea. :)