| Product | Revision | Firmware ID | Date Available | Serial Number |
|---|---|---|---|---|
| SEL-421-2 | R131 | SEL-421-2-R131-V0-Z100011-D20130627 | 7/10/13 | 1131910001 |
| SEL-421-3 | R131 | SEL-421-3-R131-V0-Z100011-D20130627 | 7/10/13 | 1131910001 |
| SEL-421-4 | R327-V0 | SEL-421-4-R327-V0-Z028014-D20200229 | 4/11/20 | ~1201020001 |
| SEL-421-5 | R327-V0 | SEL-421-5-R327-V0-Z028014-D20200229 | 4/11/20 | ~1201020001 |
| SEL-421-7 | R406-V1 | SEL-421-7-R406-V1-Z104002-D20191210 | 12/14/19 | ~1193470001 |
The Firmware IDs for older versions of the firmware can typically be found in Appendix A of the instruction manual.