Abstract: An electronic security device has at least one lock and a control center for generating keys to the lock. When a new key is generated, a new (second) combination is generated by applying a predetermined algorithm and randomly generated (first) calculation data to the previous (first) combination. To calculate a next new (third) combination, another randomly generated (second) calculation data is applied to the second combination using the same algorithm. The control center stores, on the key, the third combination, and the second calculation data used to obtain it and the first calculation data used to obtain the second combination. At the lock, the third combination is compared with a stored combination and if there is no match, the lock calculates a possible second combination by applying an algorithm, which is the inverse of the predetermined algorithm, to the stored combination using the second calculation data read from the key.

Abstract: An internal pipe cutter comprises a rotatable mandrel having a cutting drum and a guide drum mounted thereon. The guide drum is longitudinally adjustable relative to the cutting drum and controls the depth at which the cutting drum is received inside the pipe. The cutting drum includes a slidably mounted cutter which is projected outwardly into engagement with the pipe by centrifugal force. The cutter comprises a slider block having a radially adjustable cutting blade. In addition, one surface of the cutting drum has an access slot which communicates with the slider block enclosed inside the drum. The access slot allows a tool to be inserted into the cutting drum as necessary to unjam the cutter without having to dismantle the cutting drum.