Voltcraft dt 10l tachometer voltcraft 28037c70a the voltcraft dt 10l hand held instrument uses laser technology for non contact measurement of rotational speed the laser unit not only allows non contact measurement of rotating parts it is also very precise and can even be used in daylight conditions results are shown digitally on a backlit lcd display the dt 10l can be used to measure engine speed in rpm or for event counting the device is battery powered but has a connector allowing use