For every setting, the length I is equal to three times the thickness d. Each of the 250-300 grains is held between the right-angled measuring jaws of the grain vernier calliper. In doing so, the vernier calliper is adjusted to the maximum length＊of each grain. The inclined measuring slot for the thick - ness adjusts itself simultaneously to 1/3 of the length. lf the grain does not pass through the inclined slot in this setting, then it is called ≪squat≫ (favourably shaped); if it passes through, then it is ≪badly shaped≫(flatish or spiky), i, e. the ratio of length to thickness is then greater than 3:1. The quantity of the ≪squat≫ and the ≪badly shaped≫ grains is weighed. As a result, the share of ≪badly shaped≫grains is given percentage of weight of the test sample. The smaller this share is, the better the average quality of the grain shape will be.
In the assessment of grain shape described up to now in DIN 51991, the ≪lenght≫ of the grain is defined as being the edge of the smallest priam circumscribed round the grain. In the vernier calliper method, on, the other hand, the ≪length≫ of the grain is the largest dimension of the grain it has in any direction (e. g. diagonally). The grain must therefore be rotated between the right-angled jaws until the largest dimension of the grain has been set.