That bit is easy, the voltage is passed as an integer, not a float, to do that and provide accuracy to 2 decimal places the value is multiplied by 100 at source and then divided by 100 at the other end. This is done in emonHub on the emonPi for the emonPi sourced voltage, but your emonTx is sending direct to emoncms.org, so you will need to divide by 100 (or x 0.01 actually) there as it doesn’t go through emonhub.
As for why one is reading 232.9V whilst the other is reading (effectively) 244.33V could be down to calibration or put another way, the default calibration not being perfect for all devices due to component tolerances, the difference in those examples is only around 5%. It could partly also be voltage drop if one is measuring close to a load or source, like I believe you are measuring close to the inverter with the emonTx whilst at the other end of a 25mtr cable and a couple of CU’s with the emonPi. The way inverters work they do produce a higher voltage than the measured grid voltage deliberately to “tip” the power they produce towards the grid.
Do you have a multimeter with a good AC RMS voltage range ? Are you comfortable working on live wiring etc? You can confirm each device is reading accurately by checking the voltage close to where they are connected, that would either put your mind at rest they are fairly accurate or arm you with the info you need to make a small adjustment if needed.
As a sidenote, wither or both will be far more accurate than the fixed magnitude and PF Owl you are replacing.
. . . and just in case someone thinks I have crystal ball to conjour up all this info about your setup I’ll add a link here to your other thread for completeness 
. Setting up an emonPi - some newbie questions