In measurement applications many devices with two ports have different interfaces at their two ports and are commonly referred to as adapters. The interface e.g. can be a coaxial connector, a rectangular waveguide flange, or a coplanar waveguide probe tip. Two suitable methods for the measurement of such adapters are compared. The first one is a VNA measurement method using only one port calibration standards and one port measurements. It will be compared to a two port calibration method.