are they some kind of auto-increment or users steps?
the the steps are for the tax steps
if most counntries there is a step mode for taxes
thats means:
for earning from 0 to 9000$ in a year you pay 10% taxes
this is step 1 (or stage 1 you can call it like you want to)
step2 = 9000$ to 36000$ 15% taxes
.....
http://en.wikipedia.org/wiki/Income_tax_in_the_United_States
Marginal Tax Rate
[15][16][17]SingleMarried Filing Jointly or Qualified Widow(er)Married Filing SeparatelyHead of Household
10%$0 – $8,925$0 – $17,850$0 – $8,925$0 – $12,750
15%$8,926 – $36,250$17,851 – $72,500$8,926 – $36,250$12,751 – $48,600
25%$36,251 – $87,850$72,501 – $146,400$36,251 – $73,200$48,601 – $125,450
28%$87,851 – $183,250$146,401 – $223,050$73,201 – $111,525$125,451 – $203,150
33%$183,251 – $398,350$223,051 – $398,350$111,526 – $199,175$203,151 – $398,350
35%$398,351 – $400,000$398,351 – $450,000$199,176 – $225,000$398,351 – $425,000
39.6%$400,001+$450,001+$225,001+$425,001+