Final answer:
Independent checks or reference are the least often used controls to protect IT processing equipment, as they deal more with oversight rather than direct protection of the assets.
Step-by-step explanation:
The type of controls least often used to protect IT processing equipment is independent checks or reference (ind check or reference). While physical controls (such as locks and access cards) safeguard against unauthorized physical access, and authorization controls (auth control) manage user permissions and access rights to systems, independent checks are usually related to oversight and operational double-checking rather than direct protection of IT equipment. Document and record controls (doc and record), which maintain accurate records and documentation, also play a crucial role but tend to be more about the integrity and traceability of data rather than the physical safeguarding of IT assets.