Usage of Variables

1. Assign a value to a variable
-Input a variable (ex. @a)
-Push '=' button
Then '@a = ?' is displayed.
-Input a value (ex. 7 or sin(45))

2. Use variables in expression
-Input an expression including variables (ex. @a^2-3*@a+sin(30))
-Push '=' button as usual

3. Use variables to assign another variable
-Input a new variable (ex. @b)
-Push '=' button
Then '@b = ?' is displayed.
-Push del button to erase the prompt line.
And
-Input an expression including other variables (ex. @a*2-1 or sin(@a)+@a^2)
-Push '=' button

* Causion : DO NOT assign recursively with unassigned variables, which will make the app frozen !

4. Re-assign some variables to re-calc a formula
-Push '4mul' button and select a formula among popped list
-Calc it, that means, push '=' buttons several times until finish calc
And if you want to calc again with other values for some variables,
just re-assign some variables to other valuses as above and then
-Push 'hist' button on the top-left corner (not the button below character-input box)
-Choose the formula
-Push '=' button once again
This way is better than using '4mul' button again if only a few variables should be re-assigned while the latter is easier if almost all variables should be.