Thanks for your reply Trevor...
it's really the wave which create that result. It's happen when I'm trolling for landlocked salmon, at about 5km/h, in wave of about 2-3 foot. My boat is only a small 19' fishing boat, and when there is wave of only 2-3 foot, at low speed, you really feel them... So it's produce the result we can see here...
I know that I need some averaging like you said, but how to do it ? I know that I can build something to do it in excel, importing CSV data, but it's not really user friendly... Kind of big work... I want to know if we can do that in an easier way. That's the real question. Don't forget that I have tons of data.
Thanks
Fred