How to interpret lifetime score

Question

I can not understand what the following numbers mean:

Gligorić had the following record against the world champions he played against: Max Euwe +2 -0 =5, Mikhail Botvinnik +2 −2 =6, Vasily Smyslov +6 −8 =28, Tigran Petrosian +8 −11 =19, Mikhail Tal +2 −10 =22, Boris Spassky +0 −6 =16, Bobby Fischer +4 −7 =8, Anatoly Karpov +0 −4 =6 and Garry Kasparov +0 −3 =0.

I took them from here. I do understand that it tracks statistics against a particular opponent in all games, but what is this strange mathematics mean: +8 −11 =19?

Answer 1

but what is this strange mathematics mean: +8 −11 =19?

This is not mathematical notation. The three symbols are not there so you can add or subtract numbers. They mean the following:

• + is the number of victories;
• - is the number of defeats;
• = is the number of draws player achieved against an opponent;

So in the following example:

Gligorić had the following record against the world champions he played against: Max Euwe +2 -0 =5

Gligoric had 2 victories, no defeats and five draws against Max Euwe.

Against Fisher he had +4 -7 =8, meaning he won 4 games against him, lost 7 and drew 8.

Answer 2

+8 -11 =19 means: Won 8, lost 11 and drew 19