curr_items is the number of items / documents that are "Active"
vb_replica_curr_items is the number of items / documents that are "Replica"
curr_items_tot is the total number of items / documents active and replica.
If you have inserted 100 documents into couchbase,
curr_items will be 100
if you have 1 replica, vb_replica_curr_items will be 100
curr_items_tot will be 200.
If you hover over the stats in the UI, you will see the internal stat that is it using to display.
Screenshot here.
https://www.evernote.com/shard/s161/sh/a4f98d05-a2dd-4488-b92b-941a8ad53238/aa249c22e2139c7ab684a64947e89e85