The machine could be used for a treadle or as a hand crank. The base above shows a slit and holes between the storage compartment and base where the treadle belt could be fed through. Although we haven't seen one, we speculate that treadle bases were available that this base could be dropped into. The hand wheel is equipped with a pulley and groove for the belt The bolt-on hand crank has a finger that fits between the spokes of the hand wheel.
The gearing is such that the hand wheel or balance wheel is turned toward the operator while the hand crank is advanced away from the operator. Definitely designed for a right-hand person.
The needle makes three complete stitches with each revolution of the hand crank (Jim counted them!).
Our 99 makes very nice stitches. It makes a lockstitch using a rotating hook. The bobbin is easily accessible beneath the left slide.
We don't have a manual but apparently were successful in threading the machine judging from the stitches it sewed. It isn't clear how the bobbin winder receives its thread. Jim pulled a loop from the spool toward him and let it slide through his fingers with one hand and played it into the bobbin winder while turning the hand crank with the other hand. The hand wheel has a locking knob which disengages the needle during bobbin winding.