Determine typographical scale

[basham]

Minor Third (6/5 = 1.2)

[basham]

Major Third (5/4 = 1.25)

[basham]

Perfect Fourth ( 4/3 = 1.333)

[basham]

Deciding upon Minor Third.

Results in roughly:

Scale	Font Size
-1	13px
0	16px
1	19px
1.5	21px

[basham]

// http://modularscale.com
@ratio-MinorThird: 6/5;

@ratio-Scale: @ratio-MinorThird;
@ratio-Scale--05: percentage(pow(@ratio-Scale, 0.5));
@ratio-Scale--10: percentage(@ratio-Scale);
@ratio-Scale--15: percentage(pow(@ratio-Scale, 1.5));
@ratio-Scale--20: percentage(pow(@ratio-Scale, 2));

// Multiplicative inverse (reciprocal)
@ratio-Scale--05i: percentage(1/pow(@ratio-Scale, 0.5));
@ratio-Scale--10i: percentage(1/pow(@ratio-Scale, 1));

[basham]

// Typographical scales
@scale-MinorThird: 6/5;

@scale-FontSize: @scale-MinorThird;
// Shrinking scale (inverse)
@scale-FontSize--10i: percentage(1/@scale-FontSize);
@scale-FontSize--05i: percentage(1/pow(@scale-FontSize, 0.5));
// Identity
@scale-FontSize--00: 100%;
// Growing scale 
@scale-FontSize--05: percentage(pow(@scale-FontSize, 0.5));
@scale-FontSize--10: percentage(@scale-FontSize);
@scale-FontSize--15: percentage(pow(@scale-FontSize, 1.5));
@scale-FontSize--20: percentage(pow(@scale-FontSize, 2));