Phred Quality Scores

From Wikipedia: http://en.wikipedia.org/wiki/Phred_quality_score

Phred Score Translation

Phred quality scores are logarithmically linked to error probabilities
Phred Quality Score Probability of incorrect base call Base call accuracy
10 1 in 10 90 %
20 1 in 100 99 %
30 1 in 1000 99.9 %
40 1 in 10000 99.99 %
50 1 in 100000 99.999 %