A while ago I spotted something like this in an old magazine. Can't find the article or magazine back again, but it set me thinking that this would be a neat thing and quite practical to make.
An experienced typist would have no need for such a thing, but I'm not an experienced typist. This does actually help getting a feel for how far along the page I am and how many lines still to go.
The magazine picture that got me the idea was from the late thirties. Scouting around a little, this was an extra feature of a carbon paper holder. A few patents were published around that time detailing this paper page gauge, e.g. US2082494 - 'Backing sheet for manifolding assemblies', US2088039 - 'Sheet aligning and gauging device' or US3842506 - 'Spacing means and method for typing paper'.
My own page gauge (sans carbon) is designed to suit DIN A4 paper (I'm on the continent...), so must be printed on a larger than A4 sheet of paper. To make your own, this PDF file is made to print on an A3 printer. Then with some cutting and pasting (the actual, not the virtual) it'll become a basic paper page gauge.
To edit and adapt to taste or paper size, here it is also in EPS format that should load in most vector graphics editing software.
Curious if/how anybody finds this in use and what changes and improvements can be made.