If you're talking about this:

Then you might want to try this website:
LINK
Although they don't have the manual for the one you have, I would guess that the two that are listed probably use similar software and are probably calibrated in a manner very similar to that of the unit you have. Might be worth downloading one of the other manuals and trying the procedure listed there.
BTW, they are pretty good at responding to e-mail requests from what I've heard...so it might be worth inquiring via the website.
__________________
Sailingdog
Telstar 28
New England
You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Captain Malcolm Reynolds, Serenity (slightly edited)
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