I'd say around 20 years old
The two dials are timers for spot & stitch welding:-
B - D Position both timers are off so this is your normal 'continuous' welding mode.
A - C Position is for "Stitch" welding, dial A being 'on time' & dial B 'off time'
A - D Position is for Spot welding. Dial D is in off position & you set the spot timer, dial A, to give a series of spot times (in seconds).
Clear as mud?!
Best way is to have a play around with them & it will become more obvious what they do.
weldequip