Why RSSI as dBm

I'm wondering why the RSSI is converted to dBm, if the RSSI value is arbitrary, and based on the card.

http://www.wildpackets.com/elements/whitepapers/Converting_Signal_Streng...

It makes me wonder why RSSI is not simply displayed as a raw value, with RSSI Max indicated at the top of the graph, which would also give indication to the step size. A simple percentage also comes to mind.

If -50 dBm is essentially RSSI Max (i.e. 100%), doesn't the UI waste space in the graph area above -50 dBm? With lots of APs, UI space becomes important.

http://www.metageek.net/forum/inssider/rssi-level

-Bradford
. Systems Administrator
. within the College of Biological Sciences
. at the University of California, Davis