One of the essential conditions for high precision relative positioning using GNSS is resolving the double differenced carrier phase ambiguities. One method used in ambiguity resolution is the LAMBDA Least-squares AMBiguity Decorrelation Adjustment method. When using the LAMBDA method, the integer ambiguity estimation is computed in two steps. First the ambiguities are decorrelated by means of Z-transformation. Then, the integer minimization problem is solved by a discrete search over an ellipsoidal region. This paper studies integer rounding, sequential conditional integer rounding and the LAMBDA method which are integer ambiguity estimators. Moreover a numerical example is presented.