# RRD Graph Description

The graphs in Torrus are drawn by RRDtool, a powerful instrument for data aggregation and graphing.

The horizontal axis displays the time at which the data has been collected. The rightmost point corresponds to the most recent moment.

The date and time of the graph can be easily changed by using the Set date checkbox at the bottom of the page. When the checkbox is checked, the date/time string in the text field is interpreted after clicking the submit button. It is then reflected in the Report date informational line at the page displaying the graphs. The date format is quite flexible. It understands such input as "`July 13 5:00`", or "`01/13/2003 5:00`", etc.

The vertical axis scales automatically to fit the data values. The meaning of the values depends on the nature of the datasource, and is usually described in the graph legend, comments, and the help text.

Usually the legend of the vertical axis specifies the meaning of the values:

- Bps: bytes per second counter
- bps: bits per second counter
- pps: pakets per second counter

Other legends correspond mostly to gauges, such as temperature, load percentage, or disk space.

The graphing engine automatically chooses the best units for scaling the values. The scaling magnitude is displayed alongside the numerical value, with the following meaning:

- a: 10e-18 Atto
- f: 10e-15 Femto
- p: 10e-12 Pico
- n: 10e-9 Nano
- u: 10e-6 Micro
- m: 10e-3 Milli
- k: 10e+3 Kilo
- M: 10e+6 Mega
- G: 10e+9 Giga
- T: 10e+12 Tera
- P: 10e+15 Peta
- E: 10e+18 Exa

Memory usage is scaled with the base of 1024.