Calculation fail

In Windows 7, the calculator cannot calculate sqrt(4)-2, which is (√4)-2

Normally you get the answer is 0. While it is:

√4-2

=2-2

=0

Press 4.

Press the √ button.

Press - button.

Press 2 button.

Press the = button.

In Standard Calculator, you'll get -1.068281969439142e-19

In Scientific Calculator, you'll get -8.1648465955514287168521180122928e-39

By the way, sqrt(9)-3, sqrt(16)-4, etc. will get the same glitch, but different values.