x       log_10(x)   approx
1       0           0
1.25    0.09691     0.1-
1.6     0.20412     0.2+
2       0.30103     0.3+
2.5     0.39794     0.4-
3.125   0.49485     0.5-
3.2     0.50515     0.5+
4       0.60206     0.6+
5       0.69897     0.7~
6.25    0.79588     0.8-
8       0.90309     0.9+
10      1           1