I added all my gearscores (GS) and divided by 10 and it came to 622 which matched my in-game gearscore. However, this did not seem right since the gearscore is supposed to be weighted and the top three items on the weighting list are the two weapons and the chest. Those three are 625 for me with everything else lower by several points. So, my GS should be higher than the simple average.
My first thought was that the GS is not weighted. To test this I removed all my gear so that I was naked. I then equipped Weapon 1 which has a GS of 625 and my gear score was 140. I then equipped my chest GS 625 and my GS was 76. I did the same for my earring and boots both 625 and had GSs of 41 and 21. So, the GS is indeed weighted.
I built a spread sheet to calculate the normal average of my gear as well as the weighted average using the values I found via Google. It is not hard; Excel has a handy function SUMPRODUCT for this. This yielded a weighted GS of 623.3 not the 622 shown in game.
I am at a loss to explain this disparity. The only thing I can think of is that possibly the empty shield slot is being thrown in the mix. Which would make zero sense and would mean that there would need to be a second set of weights for an 11-item configuration.
Can anyone shed some light on this mystery?