Some often used graph_args:

• --logarithmic: Plot these values on a logarithmic scale. Should almost never be used, but probably more often than we do now. Logarithmic scale is very usefull when the collected values spans more than one to two magintudes. It makes it posible to see the different small values as well as the different large values - instead of just the large values as usual. Logarithmic has been tested on netstat (connection count) and some other graphs with good results.
• --base 1024: Use this for things that are counted in binary units, such as memory (but not network bandwidth)
• --base 1000: Default SI units
• --lower-limit 0: Start the Y-axis at 0 (also seen as: -l 0)
• --upper-limit 100: Use for percentage graphs, ends the Y-axis at 100 (also seen as: -u 100)
• --rigid: Force rrdgraph y-axis scale to the set upper and lower limit. Usually, the graph scale can 'overrun'. (also seen as: -r)
• --units-exponent 3: Force display unit to K, -6 would force display in u/micro.

Please see Best Current Practices - Graph scaling for more about using --base 1024.

See rrdgraph man page for more details.