Its use in the warehouse
It is the opposite of a periodic inventory, in which stock is known only when it is counted. In Mexico, the Income Tax Law (Ley del Impuesto sobre la Renta) requires companies under the general regime to keep inventory records under a perpetual inventory system (article 76, section XIV); how to comply is a matter for your accountant. A perpetual record needs counts to confirm it: without them, discrepancies accumulate unnoticed.
How Chainlink WMS applies it
In Chainlink WMS, each receipt, put-away, pick, transfer, return and adjustment updates stock by location, lot and serial number at the moment it is scanned, and it is posted to the stock ledger with its document and user. Every night, Chainlink checks that the stock ledger reconciles with on-hand stock and reports any difference.