Bristol
I have C-Map (running on Plan2 Nav), because that is what everyone had around me here in Japan.
Last summer I ran a basic check; comparing hand held compass, C-Map and depth sounder.
I understand that these results on one short run are not definitive, but this whole coastline was moved (up to 5 metres) and buckled (up to 2 metres) by the tsunami and it will years before it is all surveyed properly.
The google map photo is the narrow passage that I passed through.
The chart shows the various depths that I passed over..
I compared the depths to the contours on the chart and they were all less that a minute (in time) different.
As I say not exactly scientific, but interesting
Gary