Dell Latitude D820 laptop, lspci reports the network card as:

0c:00.0 Network controller: Intel Corporation PRO/Wireless 3945ABG [Golan] Netwo           rk Connection (rev 02)

iwlwifi driver in use, card associated via wpa_supplicant but not being
actively used

# iwconfig
wlan0     IEEE 802.11abg  ESSID:"VT-Wireless"  
          Mode:Managed  Frequency:2.447 GHz  Access Point: 00:11:20:A4:4C:10   
          Bit Rate=54 Mb/s   Tx-Power=15 dBm   
          Retry  long limit:7   RTS thr:off   Fragment thr:off
          Encryption key:<lopped out> [2]
          Link Quality=62/70  Signal level=-48 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0
# cat /proc/net/wireless
Inter-| sta-|   Quality        |   Discarded packets               | Missed | WE
 face | tus | link level noise |  nwid  crypt   frag  retry   misc | beacon | 22
 wlan0: 0000   63.  -47.  -256        0      0      0      0      0        0
 wlan1: 0000    0     0     0        0      0      0      0      0        0
 wlan2: 0000    0     0     0        0      0      0      0      0        0

Where did that -256 for "noise" come from?  It ends up confusing the
gkrellm-wifi plugin, it reports a S/N of 219dB ;)