In The Staircase Implementation (2010) and The Justice League Recombination (2010), Leonard wanted to set the thermostat above 72 degrees (Sheldon's preferred temperature), which led to quite a bit of friction. Now that they are no longer living together, Sheldon is revealed to get back at Leonard sometimes by secretly increasing the temperature on the thermostat.
This episode was taped on December 5, 2017, one day after Melissa Rauch had given birth to her daughter Sadie, which explains why she has only one scene where she is in bed.
Title reference: Amy and Sheldon use scientific measurements to decide who should fulfill which roles at their wedding ceremony.