My meters are working properly. This is my third set, so I've become a de facto expert. Power supply 6 to 12 volts AC or DC. Within the set of connectors is a counter. external terminals light up. I accidentally changed them before and didn't damage the boards. The hardest part is calibrating the counters with variable resistors on the board. Mine were blue and had an adjustment screw. They can also be silver with a small acrylic Phillips screw. You need a signal with another meter to dial it. test signal. something that checks the readings of the volumetric meter. I had to adjust my few RPMs right out of the box to get them right. If the counters jump, are weak or go to the right, it is most likely because VR1 and VR2 need adjustment. You must also be able to solder. I wanted to write a review with some instructions to help everyone before purchasing this item. Poor reviews are not fair or warranted by those who bought a product without research or proper training. Keep in mind that this is a nerd item that requires some technical knowledge. He has no "instructions". However, all connections are clearly marked on the circuit board.
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