Page 3 of 4

### 3. How to Determine Weights?

Weight selection must be done carefully to correctly reflect measurement quality. Sometimes a rigorous numeric method can be used, other times may require judgement calls based on the surveyor's experience and expertise. Weight selection is discussed in greater detail in **Chapter E** of **XVIII Least Squares Lite**.

Regardless the method used,

- weights are a reflection of random errors - the smaller the random error, the higher the weight.
- weights are relative - they indicate how much stronger or weaker one type of measurement is against other types

Providing sufficient measurements are made, one way to assign weights is by considering standard deviation. In general , a measurement weight is inversely proportional to the standard deviation squared:

Equation (G-3) |