Modern positioning methods using Total Stations (TS) use the resection from known points to the unknown observation point occupied by the TS. Resection is a function found in all TS software and this chapter is intended as an introduction to the method of resection – including a least squares solution to calculate the most likely unknown station. A Total Station measures distances and directions directly to targets set over known points. However, the TS also shows directions. The directions to the known points thus form the angle between the two known points at the observation point. Whilst we may consider this angle to be redundant information (it isn’t used in the solution by distances); it can still be used as a check of our calculations. By calculating the directions from the solved unknown point to the two known points we can get the included angle at the unknown point. But, more than a check, it can now be included in the solution of the unknown coordinates so that the coordinate values we calculate are as close to the true value as we can make, and prove, them from ALL in information available. The extra observations above the minimum required for a unique solution are called redundant observations.