| None |
- 4 x 6 microfiche only |
| * |
- 3 x 5 microcard/fiche only |
| ** |
- located in both 4 x 6 and 3 x 5 files |
| # |
- large single collections |
| ## |
- located in both 4 x 6 and single collection files |
| + |
- special 4 x 6 collections |
| ++ |
- 4 x 6 and 5 x 8 microfiche (NASA) |