Nixie Clock ITS1A Manual page 13

ITS1A CLOCK
2. Insert the 1x20 socket into the main board, but do not solder it in place:
3. Insert the 1x20 right-angled header in to the display board as in the picture below, but do not
solder (note that this is the back of the display board).
4. Insert the header+display board in to the socket on the main board:
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