I've started using calipers again just for periods of fat loss because although I like to measure waistline for progress it can fluctuate based on food in your stomach and the like. What I was wondering about caliper/skinfold readings though is don't other factors besides fat affect these as well?
It seems like they could be almost as significantly impacted, since wouldn't subcutaneous water/other 'stuff' play a roll in the thickness as well from a day-to-day basis? I could be wrong but that's what I would think, for all I know that could be insignificant though.
You're right, that's why most people just use the mirror as the gauge since it's the way you look and not your actually BF% that makes the difference (even then lighting, fullness, etc can play a role). You can also do your comparisons in the morning so you aren't full of food/liquids. Keeping other things constant, skinfold measurements can be a useful way to quantify progress (changes), but probably shouldn't be used as an accurate measurement of your body fat levels.
Yea I wouldn't be using it for an accurate bf% calculation but rather to see how the skinfolds go down. But like you mentioned it would seem like even that can be altered by water and the like. Similar to waistline measurements :\
Mirror can be useful, but its hard to judge over a period of time and lighting, distance, depletion, etc. obviously play a huge role in how good you look and unless one is very lean I think weekly progress can be hard to judge with pics/mirror.