Show ip ospf statistics - Explanation

Hi,

I confused about the output from "show ip statistics" !

##########################################################################

            OSPF Router with ID (19.19.2.2) (Process ID 1)

  Area 1: SPF algorithm executed 8 times

  Summary OSPF SPF statistic

  SPF calculation time
Delta T Intra D-Intra Summ D-Summ Ext D-Ext Total Reason
00:21:58 0 0 0 0 0 0 0 R, SN
00:15:15 0 0 0 0 0 0 0 R
00:14:47 0 0 0 0 0 0 0 R, N
00:14:37 0 0 0 0 0 0 0 R
00:14:01 0 0 0 0 0 0 0 R, N
00:12:45 0 0 0 0 0 0 0 X
00:12:24 0 0 0 0 0 0 0 X
00:11:53 0 0 0 0 0 0 0 X
00:11:43 0 0 0 0 0 0 0 R, X
00:05:10 0 0 0 0 0 0 0 R
#########################################################################

Can anyone explane what does it mean with the "Delta T" column ?
What is exactly 00:21:58 ->

Is there any way to effect this output through the "timers throttle x x x " command ?

Thanks to all..

Regards

Dennis

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