[Nexus 5 General] anactoraaron:
When I calibrate, I keep the phone vertical - which causes the image to be horizontal. The image then is -exactly- the size of my colormunki so I don't end up placing it in different places for every value. I just center it perfectly on the horizontal box (image) every time to ensure I'm not making this task harder than it should be by having it in different places every time I record a value in HCFR. Using the phone in landscape mode would bring the uniformity variable too much into play for me (like the left side of the screen in landscape being slightly brighter than the right or more blue, etc). I have gone back through after calibration with the phone horizontally, and the values are good doing it this way (although it's harder to determine where the center is).

Also, I thoroughly clean my screen prior to calibration with lens cleaning wipes and a soft cloth (gotta have something to do while it warms up), and I use a stylus to touch the screen to prevent skin, oils, etc from skewing any reading (it may not matter much, but I guess I'm a bit.. picky).

The problem I noticed this last time is with changing the first value each time before moving on to the next value (ie: change value 1 again to desired color temp and then calibrate value 5) is that value 5 seems to also adjust other values slightly (along with the recent value 1 change), and if you don't go back to those other values (2-4) they end up being off a bit (and fixing them causes other values to be off again, etc). My first time through, my first blue value was set at 128 for value #1 (every color was 436-ish). By the time I reached value 3 I needed to set blue #1 to 130 to have 6500k (+/- 10) - and value one colors were now reading 434-ish (after re-calibration). By the time I reached value 6 my value 1 needed to be 133 for blue. At that point, I decided to look at #2 for blue. Sure enough, blue #2 now wasn't right at 129, it also needed to be 134 now. ...and back and forth I went.

This past time I decided to try something a bit different, and it helped a lot. I've found it's particularly useful to 'jump ahead' when you can't seem to get the exact value you are shooting for (like my example with green being slightly off in both directions). There will be those values that you need a major adjustment to (adding 5-10 to a value when the previous ones only needed 1-2, etc), but starting with 126 for blue on all of my first 12 values made blue awfully darn close every time I went to the next value (the difference from values 1-7 is just 5 points on my most recent profile), whereas green seemed to need 2-3 points difference in the first 6 (and 6-12 afterward). Subsequently, when blue needed to be 127, I adjusted every other value 2-12 to 127, rather than leaving them at 126, and adjusted the remaining values to 128, etc when a value needed 128. Seeing these trends and 'working ahead' makes this easier (for me anyways). This is great for a first time calibration since our default setting for blue values are all too low (86 for the first value? Yeah right! 87 for #2 will also be too low!), and making large swings with future values will throw off the previous ones a bit (but you will be close still, perhaps within 5-10 for blue, 2-4 for green, and 1-2 for red). Getting this 'feel' for what your display needs to be set at ahead of time allows the calibration to be done both faster, and more accurately (from what I've found, anyway). You just need to confirm once you're done with the first 12 values that all of the values are still properly set according to the spreadsheet, as I haven't seen values 13-24 impact any of the others.

What I haven't tracked yet is the obvious next questions... like... is it just the previous and next value (or previous 2 and next 2 values) that has an effect on the value you are currently working on, etc (they are tied together as I've recently found, but how)? And... what impact does adjusting neg values have? Does adjusting the neg value 7 higher for blue make red and green brighter (a sort of adjusting from the opposite end, taking out blue to get more red and green)? The first quick go around I did with white point 31 recently (I wasn't trying to get it perfect) had different neg values than stock (as well as my first run @ white point 28. I don't know why this was, perhaps kernel related?). I did adjust the neg values in an attempt to get my black levels closer (values 17-24) but I didn't go back to see if any prior calibration changed. More importantly than that is the question of perhaps the negative values need tweaking from stock? Perhaps since all we are adjusting is the positive numbers that maybe there is a more 'preferred' setting (or ratio) for the neg numbers for each color for our calibration method (maybe everything 1-12 for red starts at 0 and goes up 15 points to value 12, then goes back down by 15 pts to 0 at value 24 and blue starts at 120 and goes up by 5 to 12 and down 15 to value 24?). There's no doubt that the neg values have an impact but what I haven't had time to figure out yet is the impact they have (across the entire curve), and the proper ways and reasons to adjust them. Maybe the neg values are too far off for me to get my black levels right which is why my final 6 values are all 1's on the pos side?

I will investigate this further over the next week and report back what I find.