Comprises a series of squares accurately engraved upon the finest plate glass by machinery. The two plates of glass (of which one form of the instrument consists), are ruled for convenience with squares differing in size. These are framed and held together by thumb screws, allowing sufficient space between them for inserting and securing a picture the size of a cabinet photograph. The lines are thus brought into such perfect contact with all parts of the photograph so that they appear to be drawn on it. One feature of this instrument which renders the square system very practical, consists of the division and sub-division of the squares by dotted lines and dash lines. The eye naturally divides a line or space into halves and quarters, and for this reason the dash lines have been designated for quartering the main lines, and the dotted lines for quartering the squares thus formed. This gives sixteen times as many squares for use as are drawn upon the photograph.

A method based on the same principle as the metroscope, but not requiring the use of that instrument, may be pursued, as follows: Fasten the photograph to a board, mark the space at the top, bottom and sides into one-quarter inch divisions, and drive sharp pointed pins in each of the division marks. Taking a spool of white thread run it across vertically and horizontally from each pin to the one opposite, and you will then have the photograph divided into one-quarter inch squares; then, if your enlargement is to be six times the size of the photograph, take the mounted crayon paper and divide the sides and top and bottom in 1-1/2 inch squares, run thread across the same as for the photograph, and then proceed to draw the outline, first in charcoal, and afterwards with the crayon. The spaces marked on the crayon paper should in each case, of course, be as many times greater than those marked on the photograph as the intended enlargement is greater than the photograph.