The box is used to power a theodolite such as the T1, T2 or T3 using one of two outlets. I have three different versions; one with a leather strap, the other two with a canvas strap. The one with the leather strap has two slots that each can take 3 C cells. The bottom slot is connected to a rheostat allowing a variable voltage to be supplied to the bottom outlet. The other slot has a direct connection to the top power outlet. One box with a canvas strap has a single slot for 3 C cells that is connected whereas the other slot is spare. The single slot is connected via the rheostat to both outlets. The other canvas strapped one is former US and has two parallel slots that both connect to both outputs. It also has two dummy batteries allowing the voltage to be either 3 or 4.5V from the same box (but not both voltages at the same time). In other words, the one with the leather strap has both constant 4.5 V as well as a variable source for lighting whereas the ones with the canvas straps are used for variable lighting. When not in use the outlets are closed by a spring to avoid ingression of dust and moisture.

I have a flaslight that can be connected to the box allowing the observer to take for example notes in the dark. The theodolite is connected using a two prong connector on both sides. Using the cabling on the theodolite the lamp(s) are then connected. In case of the T-16 the mirror must be removed and replaced with a rubber lamp shade. The shade is painted white inside for distributing the light.

The box with the leather strap came with a leather carrying bag. Whether this is original or not I do not know but the leather carries a stamp saying 'Paris' which may indicate it is not original. It does however fit the batterybox perfectly and has a separate slot for a brush and some small parts. The small compartment is kept shut using Velcro wheras the main compartment has click on buttons. The canvas strapped marked US came in its original styrofoam box. The box also contained a T21 calibration sheet which ended up with my T21.