These are buttons %, Tax, Chg, & 1/x.  You may click on these buttons or use the keyboard equivalent keys to select.

% - Keyboard Equivalent = %

The % key calculates a percentage of the previously entered number (ie. 100 + 6% = 106).

Tax - Keyboard Equivalent = t

The Tax key calculates the tax (defined in the 'Configuration' screen) of the current total (ie. 6% is defined in the 'Configuration' screen then 50 + 50 + Tax = 106).

Chg - Keyboard Equivalent = g

The Chg key is used like a cash register to calculate the change needed for the previous total.  This key is used after the equation has been totaled with the = or Enter.  Once totaled, put in an amount and click on the Chg button or press g.  Now Calc4All calculates the change needed between the new amount and the previous total. i.e. 2.00 + 1.50 = 3.50.  5.00 Chg will result with 5.00 - 3.50 = 1.50 CH

1/x - Keyboard Equivalent = r

Calculates the reciprocal (1 divided by the current number) of the current calculation window contents (ie. 2 (1/x) + 3 (1/x) = .83).