Difference between "sysUpTimeInstance (system.sysUpTime.0)" and "hrSystemUptime" SNMP MIB

Issue

• Difference between "sysUpTimeInstance (system.sysUpTime.0)" and "hrSystemUptime" SNMP MIB

• Why the uptime and snmpget command is showing different system uptime ?

[root@host ~]# snmpget -v1 -Cf -c bby-4u host.example.com system.sysUpTime.0
DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (25261518) 2 days, 22:10:15.18
[root@host ~]# uptime
02:12:33 up 3 days, 7:13, 4 users, load average: 0.41, 0.41, 0.37
[root@host ~]# date
Wed Dec 8 02:12:36 CST 2010

[root@host1 ~]# snmpget -v1 -Cf -c bby-4u host1.example.com system.sysUpTime.0
DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (1075703) 2:59:17.03
[root@host1 ~]# uptime
02:20:15 up 4:00, 7 users, load average: 0.70, 0.67, 0.57
[root@host1 ~]# date
Wed Dec 8 02:20:37 CST 2010