Speedometer calibration

Newsgroups Archive Prior to 2025
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My Datamarine S-100KL knot meter consistently reads about 1.0-1.5 knots over my GPS even taking current conditions into account. I noticed the back of the instrument has a CAL adjustment screw and I thought about giving it a tweak while underway to match my GPS speed when current conditions aren’t at play. I found the Owners Manual for the instrument on-line (attached) and it’s calibration procedure was quite complicated based on measuring distances traveled. I’m thinking the manual was written in the pre-GPS days.
Has anyone just tweaked the CAL adjustment to match their GPS speed?
Thanks in advance!

George Berntsen, Wave Dancer, 30U #283, Black Rock, CT

(attachments)

20200518_193555.jpg
20200518_193555.jpg4032×3024 1.26 MB

Datamarine S100KL knot meter.pdf (2.82 MB)

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Hi George -

I just did that on my Raymarine ST60 instrument. I used the GPS as a guide and now they are very close in synch.

Good luck!

Bob Gehrman
NS30U #396 “Quickbeam”
Baltimore, Maryland

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Just take reciprocal tracks, note average difference from GPS and trim meter up or down by that average.
Dick Lane
NS26c Port Townsend

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Thanks Bob

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Thanks Dick,