OK thanks for that...

Is it possible to do the correction in software...? ie take the dgps info from the RDS stream and the input from the GPS and then do the adjustment in the software reading from the GPS...? Or is it something that is required in the GPS internal calculations...?

The Tripmate is just a receiver with a serial cable... I have found some links to some command strings you can send it... but I think they are mostly to do with changing the format it outputs... some of the programs I have been using with it have the ability to use DGPS over IP... but maybe that info is just being ignored with my GPS if it isn't able to use it...

Cheers

Kim