I would love to see rangefinder not as new item in player equipment, but as new ship part, just like a helm. It can be damaged, it need crewmember to operate, crewmember should transfer values to gunner - all as in real world. May be not all ships should carry it, this tool looks little strange for squid, but definitly will be handy on galleon, spire, and so on.
Or, as variant, rangefinder could be set into weapon slot?
