It should be noted that in the following, a distinction is made between the test procedure, which refers to prEN 933-4, and the actual testing instructions.
At the time this cross-testing experiment was being planned, prEN 933-4 was still under development within CEN/TC 154, and it allowed the use both of vernier callipers and a particle slide gauge to check the shape of particles. In order that the participants would follow harmonised procedures in the cross-testing experiment, it was decided to send them instructions which asked them to use only the particle slide gauge, and which fixed the size of the test portions at approximately 1,7 kg for Level 1, 0,8 kg for Level 2 and 0,2 kg for Level 3.
The test procedure prEN 933-4 requires the test to be done on particle size fractions with D <= 2d and specifies the use of "appropriate test sieves". It does not specify the apertures of the test sieves nor does it give instructions about the treatment of over- or under- size, except in the case of particles <4 mm, which are not tested.
The test method is originally applied to relatively narrow delivery sizes in those countries where it forms part of the quality control system for aggregates. The specified test portion for the determination of the Shape Index is given as minimum number of 300 particles per size fraction, not as minimum mass.
During harmonisation in CEN, it was tried to adapt the method to the much wider range of delivery sizes. The test procedure had therefore to be formulated in more general terms. Also, there was a change from a minimum number of particles to minimum masses. Perhaps there was not enough time for considerations whether the amendments were clear and practical.