What is an SMM or SD Card used for?

The SMM and SD cards are non-volatile memory used to save the setup parameters and calibration for the device.  This allows the units to be powered down without loosing their setup.  These can also be swapped between like units, which allows the user to swap the unit, but install the non-volatile memory from the previous unit into the new unit.  The new unit would then power up with all the setup parameters and calibration from the previous unit, thus saving the user the time involved with re setting up and calibrating the unit.

The HI 2151/30, HI 2110, and HI 3000 series units, which include the HI 3030, HI 3010, and HI 3300, all use a Secure Memory Module (SMM). 
The HI 4000 series units, which include the HI 4050 and HI 4060 units, use the SD card.

NOTE:  SMMs and SD cards cannot be swapped between different models of units.  If one needs to be removed from one model and placed into a different model, the files should be cleared before using in the second unit.