question on byte field of NCSA common log format

Hi,

I have question on the last field (byte field) of the NCSA common log
format. For the same page access logging, the number of bytes transferred
could be varied or even return a dash or -1 for this field. Why is that?
What does a dash and -1 mean?

> grep "200 -1" access
158.182.74.148 - - [09/Apr/2001:00:14:18 +0800] "GET /images/photo.jpg
HTTP/1.1" 200 -1
61.10.43.6 - - [09/Apr/2001:00:15:24 +0800] "GET
/ehk2000/home1/eng/common/c
ontentbo.gif HTTP/1.1" 200 -1
203.173.166.69 - - [09/Apr/2001:00:16:04 +0800] "GET
/images/new_main/c_press_o.gif HTTP/1.1" 200 -1
208.151.92.247 - - [09/Apr/2001:00:17:43 +0800] "GET
/chinese/fimages/3a.gif
 HTTP/1.1" 200 -1
203.198.145.211 - - [09/Apr/2001:00:18:20 +0800] "GET /img/audioc2.gif
HTTP/
1.1" 200 -1
203.198.232.160 - - [09/Apr/2001:00:24:10 +0800] "GET /images/new_main/
c_public_o.gif HTTP/1.1" 200 -1
202.181.236.162 - - [09/Apr/2001:00:29:30 +0800] "GET /ctop.htm HTTP/1.1"
200 -1
>

Lily

Received on Monday, 9 April 2001 08:44:15 UTC