Try the following: * Replace old batteries with new ones * Make sure the batteries are aligned with the polarity in the battery compartment correctly * If you use an AC adapter, make sure the AC adapter is connected properly * Make sure the HOLD switch is switched to the OFF position. (Depending on models, the HOLD switch is usually located on the bottom of the unit.)

The information on this page applies to the following models: EXP2542/00 , EXP3460/00 , AX2400/00 .