Embodiments of the present invention provide a computer implemented method, apparatus, and computer program product for estimating, refining, and using the tare mass for an item to determine and monitor item depletion. Specifically, one embodiment of the present invention sets forth a method, which includes the steps of storing a first privilege level in a privilege map with restricted access, wherein the first privilege level is associated with a memory page used to store the content; and determining whether to permit a request to access the memory page based on the first privilege level. The retainer chassis is perpendicularly connected to the retainer main shaft and provides a rigid support to the retainer main shaft. The frequency error can be corrected based on the estimation. The multi-band RFID reader can read signals received from various kinds of tags by employing a multi-frequency band irrespective of frequency bands.