A handy person from Dutch Caribbean, Bonaire says:
March 26, 2019
Hi,
One is marked 1730.
One is marked 2430.
Top and bottom tabs are shown in photos attached.
Thanks, Bill
Paul from SWISCO responded:
March 27, 2019
Thank you for sharing your photos with us, Bill. I believe you will need the S377-18 and the S377-25 channel balances. Take a look and see what you think. If these are correct, then for the 18", go with the 1730 option and for the 25" balance, go with the 2430 option.