The Select key is used to select control of the 505 display’s top or bottom line
variable. The @ sign is used to indicate which line (variable) can be adjusted by
the adjust keys. Only when there is a changeable variable on both lines
(dynamics, valve calibration modes) does the “select key” and @ sign determine
which line variable can be adjusted. When there is only one variable per screen
the “select key” and @ sign’s position are irrelevant.