A&D GP-40K - 15-3 Using Windows Communication Tools (WinCT); 15-4 Using the WinCT software, the balance can do the following:

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External contact input
By connecting pin 18 to pin 7, or pin 19 to pin 7, for more than 100 ms, the same operation as
performed by pressing the RE-ZERO key or the PRINT key, will be performed.
Use of example
The external input connector (AX-HDB-25P/CTF)
and the foot switch (AX-SW128) are sold separately.