| IRIG-B | IRIG-B Input: The "Impulse" circuitry is replaced with the IRIG-B input. (Not available with LX-5105U/Light) |
| LIGHT | Lighted Dial: Available only on the LX-5100 Series Analog Clocks. The dial of the clock can be illuminated. A brightness control switch (or dial for non-U versions) is included. (Not available with the LX-5105U/IRIG-B) |
| P | 19" Front Panel (Rack Mount), this unit will be 4RU. |
| P2 | Dual Rack Mount: Allows two LX-5105U units to be mounted side-by-side on a 4RU Rack Mount panel. |
| UL | "UL" Approved Power Supply: The unit is supplied with a UL/CSA approved wall mount power supply. |