float arithmetic

laptop:~ pablo$ python

CASE 1:

>>> a = 987654321123456.1
>>> a
987654321123456.1
>>> (a*20 - (a-1)*20)/20
1.0
>>> (a*100 - (a-1)*100)/100
0.96
>>> (a*1000 - (a-1)*1000)/1000
1.024
>>> (a*10000 - (a-1)*10000)/10000
1.024

CASE 2:

>>> a = 987654321123456.1
>>> b = 987654321123455.2
>>> a-b
0.875
>>> a
987654321123456.1
>>> b
987654321123455.2