Depth offset for Airmar DST810

I've bought myself a new Airmar DST810. Hopefully this is more reliable than the previous one, which lasted less than 4 years.

It's installed along the centreline of the boat, around 1.5m forward of the mast. I think this is the standard position. I've calculated the depth offset to be 63cm (or thereabouts) by making a series of measurements, eventually to the waterline. This offset + the Airmar raw depth reading seems to match my plumbed depth reading.  

To be clear what I mean, the offset is the depth of the face of the transducer with respect to the waterline.

Can anyone confirm the offset measurement they use (assuming their transducer is in a similar position)? Many thanks in anticipation.

Arcadia wrote: I don’t have a measurement for you but will say that I have always used a plumbed depth to calibrate. I measure on both sides of the hull in line with transducer. Preferably on a sandy bottom as mud can give erroneous soundings. Also at a shallow depth, 8-10 ft to give the most accurate calibration where you need it most.

Many thanks indeed for this, Arcadia. I also plumbed both sides and got just a 10cm difference, so I think it's fairly reliable.