Linda writes in with a sock-related question.

Do you weigh your skeins/balls of sock yarn before you start?

She goes on to point out that she weighs her sock yarn that comes in "makes a pair" size balls (usually marked at 100g).  Because (like me) she knits for big feet, she is also often afraid that she'll run out if she makes sock #1 too large.  Weighing the remaining yarn as she knits sock #1 tells her how close she is to having used up 50% of the total. 

It's a good idea, but I don't do it.  Mostly because the lousy kitchen scale I have at home isn't precise enough for the task at hand.  That and laziness.  Also at this point, trust.  I know that a 100g ball of yarn is plenty for a pair for me, even with my clown-sized feet.  and that if I knit the foot to fit, then knit the ankle part as long as the foot, I'll have enough left over for 2 inches of ribbing.  That doesn't mean I don't get nervous.  I do.  Sometimes I do run short.  So I suppose I really should go out and buy a decent scale...

This brings up Linda's second observation.  To paraphrase:

Sometimes the ball weight is less than the label states.  My ball of Sockotta I just started is labeled 100 gms but weighed in at only 94 gms. Maybe my scale is wrong...

While a calibration or accuracy difference between any two measurement devices is always a possibility, perhaps her scale isn't wrong.  Yarn weight is measured under "standard conditions."  Presumably if Linda was experiencing the same set of conditions (most specifically - humidity), her ball of yarn would weigh the full 100g.  It's also not entirely unknown for distributors to offer products that hit the exact mark only as an over-the-lot average, with some balls being heavy and others light.  Certainly not optimal but not uncommon either.  Inconsistent yardage has been mentioned in the wiseNeedle yarn reviews (sample:  Diana, Dulce, .Manos, Melin, Tibet).   Finally there ARE some yarns that are consistently short of the listed yardage.  That's a big flaw that has also cropped up a few times in the yarn reviews posted on wiseNeedle (sample:  Superwash 12 Ply, Nature Cotton). 

Should one expect every skein to hit the 50g or 100g (or whatever mark)?  Under ideal conditions, yes.  But I doubt it will happen often in our imperfect universe.  My solution to the problem is on larger projects - to buy that extra skein as insurance.  I've dipped into my insurance yarn often enough to make it a standard part of my yarn purchase planning.