| Number | Name | Date | Kind |
|---|---|---|---|
| 4286325 | Dlugos et al. | Aug 1981 | |
| 4301507 | Soderberg et al. | Nov 1981 | |
| 4466079 | Daniels et al. | Aug 1984 |
| Entry |
|---|
| Torrance et al., European patent application EP0019515A2, "Electronic Postage Meter Having Improved Security and Fault Tolerance Features". |