It's not possible to type numbers with + prefix like +5
It's not possible to type operation like 5--5. Instead, use 5+5
Dividing by 0 will result in displaying Error message
Input is limited to the 7 characters including
Maximal input value can be set to 9999999 or 99999.9
Minimal input value can be set to -999999 or -9999.9
Press * to remove the last typed input. It can be used multiple times to revert more than one input value.
It is possible to recall the last typed operation by using the * key. First you have to clear the current input, and then press the * once again.

123+
322 <- start pressing `*`
32
3
    <- empty input field, press the `*` once again
123+

Trying to execute operations without right operand will trigger displaying Error message, i.e. 100+=
There is no support for typing values using scientific notation, i.e. 10e9