A device for determining the tightness of a wedge used to close the slot of a dynamoelectric machine and firmly restrain the conductors installed in the slot, is in the form of a tapping hammer or similar tapping tool. The heat of the hammer contains an accelerometer which outputs a pulse signal having a duration representing the time the head is in contact with the wedge. The pulse signal duration is also related to the tightness of the wedge. Associated electronic circuitry measures the time duration and displays the measured value on a digital display on the hammer unless this display is inhibited. The strength of each blow is assessed by an integrating circuit which gives an output related to the strength of the blow. If this output is not within predetermined upper and lower limits, defining a "window", the display of the measured time duration is inhibited and instead the display indicates that the blow was too hard or too weak. The operator quickly learns to strike a wedge with a force that is within acceptable limits, i.e., within the "window". The display is reset each time a new blow is struck. The device is battery powered and portable and preferably the display shuts off if there is an inactive time duration, say 30 seconds, after one blow is struck.