I bought two new GPSs, Columbus V900 and V990.
Both have mtk2 chip, with -165dbm sensitivity.
I had an V900 before, but I lost it.
That one has -159dbm sensitivity.

The new GPS both have this drifting problem.
Please see the following two graphs.
Two tracks in first graph are recorded when walking, on different days, but with all other conditions the same.
The GPS was put in my pocket, facing horizontally, not upwards.
One track falls on the real positions where I walked.
But the other one differs a lot.
The place is beside a lake where the GPS has clear view of the sky.
The second track was recorded around a residential block.
Track 1 was recorded when driving. The GPS was on dashboard under wind shield.
Track 1 follows the route precisely.
Track 2 was recorded when walking. The GPS was in my pocket as that in first graph.
Track 2 follows the real route pretty well.
Track 3 was recorded while coming back following the same route.
So track 3 should be identical to 2, but it is not.
Track 3 goes directly through the block and doesn't show the 90 degree turn at all.

Is this position drifting normal?-track-2.jpg

Is this position drifting normal?-track-3.jpg

I wonder:
1. Whether this position drifiting is normal, because of the high sensitivity of the mtk2 chip.
I didn't have this problem with my old GPS in 7 years, but maybe that's because it has lower sensitivity?

2. Whether this drifting has something to do with the GPS antena orientation?
I feel that the drifting is only serious when the GPS is not facing upwards.