fieldname.cdef
Fieldname.cdef allows you to manipulate the data collected in an rrd. Things like turning bytes into bits, making numbers negative, and a host of other operations.
Usage
In this example down_bytes is the fieldname, and we are multiplying 'down_bytes' by 8 in order to get bits. The operand,operand,operator notation is know as Reverse Polish Notation.
down_bytes.cdef down_bytes,8,*
This can be used to accomplish any number of tasks. Such as Taking a number reported as Milliseconds and changing it to Sec, then making the number negative to display on the bottom of the graph:
time_ms.cdef 0,time_ms,1000,/,-
