So I was a bit underwhelmed with the histograms in livelink and HP tuners so I wrote my own software package to plot 3d graphs.
My software has the addition of working out average, min, max and standard deviation per cell. If you standard deviation is high due to large span of data the average value is kind of meaningless.
You can then trend the data in that cell vs a 4th variable, manifold pressure is usually the problem. If you see your fuel trims go lower as the pressure goes lower you know you have a problem with the offset not the slope.
Basically it makes it really easy to tell if you should be adjusting offset instead of slope.
Here are some screenshots of some old data I had which had terrible trims on low load.
Standard deviation view:
Count view:
plotting the actual value against a 4th variable (MAP in this example)
As you can see from the last screenshot there is a large standard deviation in cell 10 degrees cam at 2000 rpm. You can see at very low MAP of 5kPa there is a trim close to 0.84 and at higher map values it trends to 1.00, this indicates there is an offset error, not a slope error.
Tweaking the "map at zero airmass (high res)" value would fix this issue, opposed to tweaking the "MAP per airmass (high res)" value which would simply shift the error.
I'll post a link up to the beta software shortly