Datamarine
I have a Datamarine Knotmeter. If that is the instrument you are referring to, let me know what info you need regarding its operation. You might also want to contact DMI and see if they can help:DMI Marine, Inc.18 Commerce Park RoadPocasset, Ma 02559main phone number: 508-564-7491fax number: 508-564-7497email: dmifix@dmimarine.comAlso, link below.