Another way to indicate the correct orientation of a slide is to draw a line
diagonally across the top of the slide mounts as you hold them all together.
If a jagged line occurs in this diagonal, you know that a slide is missing.
This procedure works primarily for canned slide shows that rarely change.
Figure 2-30 shows the procedure for marking a stack of slides with a
Figure 2-30. Marking slides with the diagonal line method.