Bias

It implies systematic distortion arising fromsuch sources as a flaw in measurement oran incorrect method of sampling.

• Difference between true value and the measured
• Inaccurate
• systematic error affecting all the measurements

Eg.

• Instrument not properly adjusted
• Measure of 100-ft units with a tape only of 99-ft long
• Under-estimation of tree height by timber cruisers consistently
• Arbitrary shift of field plot locations to capture typical samples

Accuracy

Accuracy refers to the success of estimating the true value of a quantity. True value can be determined only by very careful measurements with accurate instruments and formula used. As to the Forest Mensuration, although mensurationis a branch of mathematics, Forest Mensuration does not attempt to secure absolute mathematical accuracy. Forest Mensuration aims at reasonable and relative accuracy, i.e. maximum accuracy which is profitable and possible to obtain in practice.The reasons are:

• Characteristics of trees
• Varying methods and conditions of felling and conversion
• Personal bias of the estimator
• Biological character of the forest
• The use to which the measurements are to be put
• Cost

Precision

Precision is the degree to which measurements approach or estimate the average. It gives consistent results from repeated measurements, e.g., 4.44 is more precise than 2.4

In short,

If target is directly hit the centre, that shows the absolute accurate, If it hits to the middle circle (>50% to 99.9999%), it is precise. If target hits in outer circle then it is bias (< 50%)