The diagram (right) shows the basic parts of the modern plough: 1  beam. 2  hitch (Brit: hake) 3  vertical regulator. 4  coulter (knife coulter pictured, but disk coulter common) 5  chisel (foreshare) 6  share (mainshare) 7  mouldboard.
Non-probability sampling is a type of sampling technique whereby all the units of a population do not have an equal chance of being selected in the sample.
In a non-random (or non-probability) sample some units of the population have no chance of selection, the selection is non-random, or the probability of their selection can not be determined. In this method the sampling error cannot be estimated, making it difficult to infer population estimates from the sample.