how come i didn't get 100 percent accuracy?

so in this game i played 5 "book moves" and 5 "best moves" but the computer only gave me 99.7 accuracy... why?

Chess.com preferred 7. Bxg8 slightly over your move of Qb3.  And by "slight", I mean very, very slight:  a difference of 0.02! 

(Because the difference is so small, it gives in the test that 7. Qb3 is a "Best Move" even though it prefers an alternate move.)

thanks for info! i was so close to the elusive 100 percent accuracy, i will remember this next time my opponent plays f6

Quoting chess.com "Your 'accuracy' is a measurement of how closely you played to what the computer has determined to be the best possible play against your opponent's specific moves."

Books move are theoretical movements, but that does not mean that the computer thinks they are the best moves.

are you saying that the computer may lower your accuracy if you play subpar "book moves"?

I think so

I never got even close

looks like your right. Ke2 against the sicilian give like a 1 percent score despite being a book move.

btw i ran Bxg8 by the computer and it still gave me 99.7

Actually, it's the other way around. If you play only book moves you will get 100% accuracy. Best moves are the ones that lower your accuracy.

like i said above i played ran a two move game by the engine and it gave aprox 1 percent accuracy despite both being book moves... so seemingly you are mistaken

you probably scolar mate

my highest is 97.0

in 22 moves

I think book moves aren't necessarily the best moves all the time, because for example 1 a4 is a book move and it gives almost a pawn advantage to black on move 1.

yeah...

97.7 for me in 3min blitz ~30-40 moves

uh i am only 1180-1200....

"book moves" really mean little. Quite often "book moves" are not the best moves.  Sometimes "book moves" are mistakes.  

The lower the strength of your opponent --the less this whole idea of "accuracy" means.

At best your "accuracy" rate will give you some indication on how well you played.

In the game per this forum the chess engine made very early mistakes which it claimed as its book moves.

the engine claimed that mistakes are best moves??

Rorschach   yes that sometimes happens.

But mainly what I was trying to say is that often "book moves" are mistakes.