This is the BK-100 bug and a descendant of early Japan-made Swallow bugs.
It has a flat pendulum like the Vibroplex Champion. Adjustments are fitted with locknuts and face
inward so the complete mechanism can be protected by a mating clear plastic dust cover. A
single fingerpiece extends from the dust cover's far end, and a small hole in the key cabinet's side
permits routing an output cable to a transceiver. The base is well weighted and uses four suction cup type
feet. Apparently Hi-Mound of Japan made and old and new style. The old style didn't use pressed
parts except for the yoke, and the screws nuts are different from the new one. I have found that alot of
these bugs are missing the plastic dust cover or they are cracked...