A device management system comprises a processor, a data storage device and a network connection. The data storage device stores weighting data associated with at least one ATM. The processor receives performance metric data from the ATM via the network connection and accesses the weighting data from the data storage device. The processor weights a portion of the performance metric data associated with the ATM with respect to a portion of weighting data associated with the ATM, to produce weighted performance data. The weighted performance data is used in estimating the number of customers unserved during a period of downtime of the ATM.