Sampling theory and practice
Be sure to check the orientation of the cone splitter daily: While a cone splitter should and generally will give a matched (equiprobable) pair of field duplicates, the orientation of the splitter is all-important in determining this. The long axis of the splitter needs to be vertical and the widest part of the splitter, i.e. the join between the cone and the chute, needs to be horizontal. This should be checked daily with a magnetic clinometer.