spy; secret agent

armour havelock / helmet neck guard

a jo: a fighting staff, a little over 4 尺 (shaku, “a traditional unit of measure, about 30 cm or a foot”) long, shorter than a 棒 (bō, “quarterstaff”)

tuning (the adjustment of a system or circuit to secure optimum performance) / tuning (the calibration of a musical instrument to a standard pitch)