Let it be supposed that the custom in a factory is to test a yarn by unravelling a length of 20 yd. and finding the weight of this in grains. In each calculation the proportion will be repeated of finding the number of yards in 1 lb. or 7,000 grains. Again, if the prevailing counts be worsted, then this will involve 560 in each calculation as in the following example.
Example 1.—On unreeling a yarn it is found that a length of 20 yd. weighs 10 grains, find the counts in worsted.
By proportion, if there are 20 yd. in 10 grains, the yards in 1 lb. or 7,000 grains will give the yards per lb. This obtained, we divide by 560 the length of the worsted hank to obtain the counts thus—
| 20 × 7,000 | |
| = 25's worsted counts of yarn. | |
| 10 × 560 |
Example 2.—A worsted hosiery yarn is tested and 20 yd. are found to weigh 35 grains, find the counts.
| 20 × 7,000 | |
| = 7⅐ worsted counts. | |
| 35 × 560 |
If these two examples be observed it will be noted that for every calculation of this type such as a yarnman might be expected to make frequently, the common numbers are 20 × 7,000
560 = 250. These will occur in every calculation of this kind and this gives a short method of getting the result, for in place of using these three factors we take the resultant 250 as shown and divide the weight of grains into it.
Example 3.—Find the counts of a cashmere hosiery yarn, 20 yd. of which weigh 24 grains.
Following the method indicated we can obtain this result at once by dividing 250 by 24 = 10·4 counts cashmere.
The other counts met with frequently is the cotton or merino system where the hank number is 840 and the value in all such calculations is given by the numbers—