No doubt
one of the many different models of Sun distributor machines; a unit that spins the distributor with connections to a strobe light to indicate each "spark". There are various gauges--Tach, Dwell, Vacuum (and a vacuum pump for testing the vacuum advance) and an ohmmeter for testing points resistance.
The strobe shows against a degree wheel, you can verify cylinder-to-cylinder spark variation.
The "Hot-rod" usefulness is in verifying the centrifugal and vacuum advance curves as a function of distributor RPM or vacuum level.
They were in use with better shops (and schools) in the '40s, '50s, '60s, and began to die-out in the '70s, even before cars got distributorless ignitions. Electronic ignitions made distributors so "trouble-free"
that no one bothered to pull them out for testing. My high-school auto mechanics class had a Sun, the Sun I bought came from a Vo-Tech (High school?) in Utah.
I had a very compact Allen distributor machine; sat on a table-top--about the size of a typical stereo receiver, but taller to support a Chevy distributor. Damaged in a garage fire. I bought a full-fledged Sun unit to replace the Allen. The Sun machines are physically larger than my old Allen; and mostly they're parked on a dedicated cabinet that holds various supplies--a magnetic-pickup amplifier for electonic ignitions, fresh sets of points, various distributor tools, an adapter for Flathead Ford distributors, and perhaps a rack of eight spark plugs for verifying the actual sparks made by the distributor (kind of a teaching tool for students, not really useful otherwise.) My Sun is usable, but kinda wounded--the strobe is no longer bright and stable. No doubt the electronics that power the strobe need some lovin'.
Photos of various Sun models, shamelessly stolen from the internet:
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