The entire story is extensive and most of it is told herein. Quickly updating, I have tuned a functioning EPHOD, that is to say Aaron's Breastplate and the Urim and Thummim from the Bible. This device was used by Samuel to discern that Jesse was holding out, not bringing forth David as the successor King after Saul, in Israel.

Name:  EPHOD on MERKABAH bag.jpg
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Name:  EPHOD Manna Qetoret Stones ENKE chakra stones.jpg
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To better understand, resort to Sir Laurence GARDNER explaining the gemstones as a circuit.