Negative market depth - how is it possible?

[grandia3]

Looking at today PDN's market depth
04:29:44 PM 2.870 -900
04:29:43 PM 2.910 -1,100
04:29:31 PM 2.790 -611
04:29:31 PM 2.790 -750
04:29:26 PM 2.790 -599

how is it possible to have negative there?

 

[skyQuake]

Looking at today PDN's market depth
04:29:44 PM 2.870 -900
04:29:43 PM 2.910 -1,100
04:29:31 PM 2.790 -611
04:29:31 PM 2.790 -750
04:29:26 PM 2.790 -599

how is it possible to have negative there?

Reversals - note how its after 4:10pm
Bad trades and stuff get reversed.