Using clippers is difficult with only two hands and frequently causes soil contamination. With a helper, clippers can speed things but avoid using rusty or dirty ones. Soil, weeds, dead herbage and other forms of pollution such as perspiration can distort the results. So people have to wear thin plastic gloves to avoid sodium pollution from perspiring hands. After washing your hand, don't wipe your brow with your collecting hand.
Plants have varying levels of some elements in different parts.
For example, leaf tips have more P, but less Ca, so if only the tips of leaves were collected, P would be inaccurately high and Ca inaccurately low. Aim for 6 inch long leaves. If sampling 3 inch pasture, only leaf tips can be collected, so inform us to allow for this in the reading of the figures. At seeding, many leaf levels decrease as the elements move to the seed because the leave have finished their job and are ready to die. Element levels also vary with the weather and season, but these trends are known and allowed for.