Thanks Steve.

I will design and build a PIC-based interface which will deliver
NMEA-formatted proprietary sentences containing the current rates from
the two Sonic Speed systems. Others will organise for these data to get
to our servers via various boxes of tricks and WiFi. The data from these
will be logged, and probably be made available in real time via the
Internet.

Steve Lusardi wrote:
You couldn't afford the Sperry unit anyway.......it is very expensive.
From your comment, I assume you don't have the rest of the system
(processor and display) How are you going to use it? I will find an
impeller measure it and get back to you.
Steve