This simplification isnt without consequence as there is an error term that greatly reduces the measurement range compared with the standard 2-port transformation. The error can be calculated as:
The error is shown graphically in Figure 3 indicating that an error of +4% exists for resistance values below about 25m and a -5% error is exists for resistance values above 2.37. Despite the greatly reduced measurement range, the resulting range is quite usable in many applications. The resistance can be increased using a modified 2-port measurement. 
Figure 3: Measurement error as a function of the resistance being measured. The maximum error due to calibration is +4% and -5% corresponds to a resistance value of 2.37.