Modern-day VNAs provide a wide range of calibration choices. The choices stem from the different operating and measurement conditions, which present increasing challenges for providing accurate calibration standards. Probably the most central concept to making good vector network analyzer (VNA) S-parameter measurements is the calibration. This application note will discuss the Line-Reflect-Line (LRL) method of calibration and will include LRM (Line Reflect Match) and a new alternative algorithm providing a more precise termination model developed by Anritsu and designated ALRM (Advanced Line Reflect Match). After a description of the theory and practicalities of an LRL calibration, examples will be provided with emphasis on the Anritsu 3657 LRL Calibration Kit in conjunction with the VectorStar VNA.