Show Score - question about critic ratings

I understand Show Score to be a sort of Rotten Tomatoes for theater. Online users can write their own reviews and give shows a rating out of 100. How do they calculate the numerical scores from critics? I feel like I've read a few reviews linked on Show Score and I wouldn't necessarily agree with the numerical rating that's been assigned.

Just wondering. Thanks.

NEW REVIEWS FROM CRITICS YOU ARE FOLLOWING 
Click on the shows to read their reviews.

Ben Brantley of The New York Times gave Grief Is The Thing With Feathers a ShowScore of 85. Details

Ben Brantley of The New York Times gave Beetlejuice (Broadway) a ShowScore of 45. Details

Ben Brantley of The New York Times gave Ink a ShowScore of 85. Details

Ben Brantley of The New York Times gave The Pain of My Belligerence a ShowScore of 65. Details

Charles Isherwood of Broadway News gave Beetlejuice (Broadway) a ShowScore of 70. Details

Charles Isherwood of Broadway News gave Ink a ShowScore of 85. Details

Charles Isherwood of Broadway News gave Tootsie (NYC) a ShowScore of 85. Details

Wow, that Brantley score for Beetlejuice.