The first interval is,Originally Posted byd.darbyshire

28.9-3.8,28.9+3.8

Which is,

25.1,32.7 This takes 68%

The next interval is,

25.1-3.8,32.7+3.8

Which is,

21.3,36.5 This takes 95%

The next interval is,

21.3-3.8,36.5+3.8

Which is,

17.5,40.3 This takes 99.7%