The sub-unit number within module in slot 'n'. For each non-empty slot there will exist a module entry with a chasModuleSubUnit value of base. If the chasModuleType of that chasModuleEntry is hsm, then there may be additional chasModuleEntrys with the same chasModuleSlot value but with chasModuleSubUnit values of hsm1, hsm2 or csm3. These are HSM or CSM-U sub-modules. An HSM module can have up to 2 daughter cards on it. The first position would be denoted by hsm1(2) and the second position is hsm2(3). A CSM-U module can have up to 3 daughter cards on it.The first position would be denoted by hsm1(2) and the second position is hsm2(3) and the third postion is csm3(4).

The general implication of this field is: each occupied slot will have an entry field will be base(1), and may if the module supports daughter cards have entries for which if this field is hsm1(2), hsm2(3) or cms3(4), corrosponding to an installed daughter card on the HSM or CMS-U in the specified chasModuleSlot. (and the card type will be listed in chasModuleType).