The available one letter functions are:

@table @code
@item -
Negates the argument.

@item U
The absolute (unsigned) value of the argument.

@item S
Strips the commodity from the argument.

@item A
The arithmetic mean of the argument; @samp{Ax} is the same as
@samp{x/n}.

@item P
The present market value of the argument.  The syntax @samp{P(x,d)} is
supported, which yields the market value at time @samp{d}.  If no date
is given, then the current moment is used.
@end table