Why Don't the Calculated Percentages Add Up to 100%?
Problem: When adding up the percentages calculated by the program for a sample's sand, silt and clay, the total does not add up to 100%
Explanation: You had material left sitting on top of your largest sieve. The software cannot classify that material -- all it knows is that the material is larger than the largest sieve's opening diameter, so it could be gravel, cobbles, boulders, etc. Whenever this happens; i.e., whenever you have less than 100% passing your largest sieve, there's no way for the program (or a human engineer) to put an upper bounds on your material: the contents of the material retained on your largest sieve simply cannot be categorized.
Solution: The "proper" solution would be to re-run the test with a large enough top sieve that everything falls though so that you can establish an upper bounds on your particle size. Alternatively, while we don't advise clients to estimate data, if you are certain that none of your material is larger than, for example, 3", you can enter a 3" sieve into the program that has 0 grams retained.