I have some GPS simulation software that can send GPS data to MeHere via some virtual serial port software. I have noticed that if I just send a GGA to MeHere every second then I get no lag effect. MeHere position updates on screen at a 1s interval. However, if I now add in an RMC string then the MeHere update rate falls to 2s and the plotting starts to lag by 1s every 1s. As most GPS receivers will output atleast the GGA and RMC strings, then this could be a reason why we see the lag. Maybe!