Wei Ming from singapore wrote:
Sometime the calculation is not accurate, Eg:
11.12 - 10.5 = 0.62
but i get 0.619999999999999
Is it system error or regional setting's problem

Neither. The problem is two-fold:

1. The displayed values are probably rounded, if they are the result of
a formula. For example, "11.12" might be any value between 11.115 and
11.1249...9. You can confirm this by formatting Number with many
decimal places (Format Cells Number).

2. Binary computers cannot represent most fractions accurately. So
even if you type "11.12" into a cell and Excel displays "11.120...0",
the value in the computer is not exactly 11.12. Excel makes
adjustments when evaluating some formulas in an attempt to hide these
anomalies. But it is not unusual for the "inaccurate" representation
to have visible consequences.

You can usually compensate by using ROUND() judiciously.