This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
In trimming small photograph prints I experienced some difficulty in getting them square, and I did not care to invest in a trimming board. By following a line drawn around the print with a triangle, it was impossible to make a perfect rectangle. In the place of a trimming board I now use a piece of glass cut a little smaller than the desired print. The edges of the glass are smoothed by filing or grinding them. In making a glass, be sure to have the corners cut at perfect right angles and the edges ground straight.
The glass is easily located over the print, and by holding the two tightly together the edges of the print can be trimmed with a pair of shears. - Contributed by E. Leslie McFarlane, Nashwaaksis, N. B.