The digits (left 2) on the Standard DS10 depth sounder Head Unit were bad. All I could read was the right digit, so I was getting only 10th of a foot readings in shallow water.
I did not want to pull the boat out to put in a new through hull transducer. Plus they cost $.
So I had to get a compatible Head Unit. This was done by going on e-bay and finding a STANDARD HORIZON QUARTZ DEPTH SOUNDER, P/N 86U051110, Model DS-20 Head Unit. Total Cost $14.50 with shipping.
It worked.

Same connections as the old DS10 unit, including the same output frequency and power. Mounting is different, but I can live with that.
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bristol built in 1972 by Bristol Yachts, Inc. and designed by Halsey C. Herreshoff has lenght over all 26, length on waterline 21'10'', beam 8', keel draft 3'10'', ballast #2400, displacement #5700, sail area 327 sq. ft.,