Some PCB will have a "stair-step"; each layer labeled with a copper number and cutouts in the other layer to be able to see it.

Cut the board in half and inspect the copper, the layers of PCB is the same as the layers of copper.

Using a bright light, it's easy to see if a board has inner layers even if it doesn't have blind vias.IF the board have inner layers,it will be a multilayer PCB,otherwise it is not. But for this way, we could not know the exact layers of the board.

I was burnt by layer numbering today,my layer number "1" is mistaken as a marker for pin 1 on some nearby connector.

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