Hi! So the equation is based on general math rules. Which can be shown below:

Conventional Order of Operations when calculating equations

1. Brackets (Parenthesis)

2. Exponents

3. Multiplication and Division

4. Addition and Subtraction

What does this mean?

First example: if you recharged 5000 ingots, you will get the equation below:

170 + (x-1000) x 30% = Rebate (Where X is your recharged amount)

This means your rebate for recharging 500 would be 170 + (5000-1000=4000) x 0.3 = 170 + (4000 x 0.3) = 170 + 1200 which is 1370 in rebate.

Second example: if you recharged 6000 ingots, you will get the equation below:

1370 + (X-5000) x 40% = Rebate (Where X is your recharged amount)

This means your rebate for recharging 5001 would be 1370 + (6000-5000=1) x 0.4 = 1370 + (1000 x 0.4) = 1370 + 400 which is around 1770 in rebate.

Hope this helps!