S7 is a glass slide 75mm x 26mm (3 x 1") marked over the top surface in a way that a referenced position can be directly read relative to the locating edges. That means it is marked with a square grid at 1mm intervals. Each square contains a center ring bearing reference letters and numbers. The remainder of the square is subdivided into four segments numbered 1 to 4.
Reference numbers run horizontally 1 to 75, and letters vertically A to Z (omitting I). The main locating edge is the bottom of the slide, which is used in conjunction with either the left or right vertical edge of the slide.
All England Finders produced for over 40 years are identical. The purpose of the finder is to give the microscopist an easy method of recording the position of a particular field of interest, so that another person in another laboratory can relocate at a later date, or the same position, or when using any other England Finder on any other microscope.
The location of the arrows is identical for all England Finder slides. Mark a label on the left hand side of the specimen slide indicating the orientation to be repeated. By replacing the specimen slide with England Finder, taking care not to disturb the position, feature of interest can be noted. The feature can also be relocated at another place or time by reversing the procedure. A total of 100 positions on a slide can be accurately located.