Dales,

Thanks for your input. It's good to know that I'm not alone!

Although the error isn't huge it can be a pain....

eg. Last weekend I did the Fairfield Horseshoe in the Lakes. The final part of the descent went down the east bank of Rydal Beck, the river that drains the horseshoe. The river runs almost exactly north to south. The Memory Map error results in the track appearing to go down the west side of the river much of the time with a few unlikely river crossings thrown in for good measure. It's not a track I'd want to print off for a map-and-compass-only friend.

I'm keen to learn why Memory Map is slightly out, but Google Earth and Garmin Topo UK seem to be OK.

I'll watch this space....

Cheers

Geoff

Jason,

Thanks for your help so far.

I've just carefully checked my Memory Map OS 1:50k Great Britain map.
------------------------
Map details
Name: OS 1:50k Great Britain
Long title: OS 1:50,000 Great Britain
Edition: 2006
Revision: 2
File name: os50_gb.qct
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It also shows a slight error at the Scafell Pike grid line intersection I mentioned earlier.
Waypoint with grid ref: NY 22000 07000 is slightly off to the west of the grid line intersection.
Waypoint with grid ref: NY 22014 06997 is bang on the grid line intersection.

My OS 1:25k - Lake District Memory Map definitely benefits from a WGS84 datum shift of 6 metres North and 15 metres east. This helps keep all the grid line intersections closer to the nice round numbers that they should be. My Garmin 76CSx tracklogs also line up more accurately when this datum shift is applied to the map.

I know for sure that these are both official Memory Maps as I own both the discs they came from.

Do you know why these small registration/calibration errors exist?

All insight gratefully received.

Cheers

Geoff