Bivariate data often arises from the use of two different techniques to measure the same quantity. As an example, the accompanying observations on hydrogen concentration

(ppm) using a gas chromatography method and concentration using a new sensor method were read from a graph in the article “A New Method to Measure the Diffusible Hydrogen Content in Steel Weldments Using a Polymer Electrolyte-Based Hydrogen Sensor” (Welding Res., July