The preceding example shows that weights used in kriging involve not only the semivari ances between the point to be estimated and the known points but also those between the known points. This differs from the IDW method, which uses only weights applicable to the point to be es- timated and the known points. Another important difference between kriging and other local meth- ods is that kriging produces a variance measure for each estimated point to indicate the reliability of the estimation. For the example, the variance estimation can be calculated by