Odd Yarn Count Numbers

In a comment on an earlier post, Neki kindly pointed me to a website that lets you convert from one yarn count system to another (for example, from tex to cotton count or from worsted count to NM). Unfortunately, this site requires that you know what count system is being used on the stuff you want to convert. And with the mystery cones of fine cotton, the numbers just don't make sense in any count system I'm familiar with.

I tried out the conversion to see if the old cones were labeled in a tex system. Nope. In the tex system, a larger number is a fatter yarn, and something with "600" in it's label would be rope, not something in the range of sewing thread.

So, today I got out the McMorran Balance and weighed out two of the mystery yarns. The one labeled 500/3 comes in at 14,000 yards per pound. The one labeled 600/3 comes in at 16,000 yards per pound. (Both close to the range you'd expect from good old size 50 sewing thread.)

Using the standard cotton count of today, a 50/3 cotton is 14,000 yards per pound. Does this mean that some decades ago, the mills all agreed to drop a zero off an old style count system? I'm still mystified, but at least I now know the yards per pound of these yarns!