Q.If the diameter of the pulley is 6 inches, length of pointer is 10 inches and distance travelled by pointer is 5 inches, calculate the actual growth in length of plant.

Because plant growth is usually too slow to observe directly, it has to be measured with dedicated techniques and expressed through defined parameters - increase in length or girth, increase in fresh or dry weight, increase in area or volume, or an increase in cell number. The arc auxanometer is the classic mechanical instrument for measuring stem-tip elongation: a thread tied to the growing tip runs over a small pulley to a hanging weight, and a long pointer fixed to the pulley's axis sweeps across a graduated arc as the pulley turns, magnifying a small amount of real growth into an easily readable pointer movement. The actual growth is then calculated back from the pointer's movement using the relationship: actual growth in l …