A handheld distance measuring instrument includes a first emission device, a first reception device and a second reception device. The first emission device is configured to emit an optical measurement radiation onto a target object. The first reception device is configured to detect the radiation returning from the target object. The second reception device is configured in order to detect a reference radiation internal to the instrument. The reception devices respectively include a first detector unit, a second detector unit, a first time measurement unit, and a second time measurement unit. The first time measurement unit is configured to be connected selectively to the first detector unit and to the second detector unit. The second time measurement unit is configured to be connected selectively to the first detector unit and to the second detector unit.