A soil's water holding capacity is the difference between field capacity and wilting point. For more information get suggested capacities by soil or by crop type.
The maximum net depth of water per irrigation is defined by how much water a soil can hold without losing it to leaching. If the soil is full of water, the crop can use this much water before it is stressed. The move interval assumes a maximum set time on only 12 hour intervals because it is less work. A good estimate for a set-move sprinkler ranges from 50 - 75%. The suggested nozzle diameter assumes that the nozzles are in good condition, and are all the same (All DuCaR Sprinklers come with FREE nozzles suitable with the sprinkler).
Reference: Washington State University