When mongostat is run with multiple hosts (either with the --discover flag or -h), the number of operations appears to be divided by the sleep time.

To reproduce:

Here is a JS function that will insert 100 records per second for a minute:

> for(var i=0; i<60; i++){for(var j = 0; j<100; j++){db.stattest.save({t:i, x:j})};sleep(1000);}

While the above is running, run mongostat with the following options:

$ bin/mongostat -h localhost,127.0.0.1 5
insert query update delete getmore command flushes mapped vsize res locked % idx miss % qr|qw ar|aw netIn netOut conn time
127.0.0.1:27017 20 0 0 0 0 1 0 464m 3.35g 9m 0.1 0 0|0 0|0 1k 1k 8 11:56:23
localhost 20 0 0 0 0 1 0 464m 3.35g 9m 0.1 0 0|0 0|0 1k 1k 8 11:56:23

Notice that the number of inserts is 20 (100/5). The same can be observed with using --discover:

$ bin/mongostat --discover 5
insert query update delete getmore command flushes mapped vsize res locked % idx miss % qr|qw ar|aw netIn netOut conn time
localhost:27017 20 0 0 0 0 1 0 464m 3.35g 8m 0.2 0 0|0 0|0 1k 1k 8 11:56:45

If an interval of 10seconds is used, the "inserts" count changes to 10 (100/10):
$ bin/mongostat --discover 10
connected to: 127.0.0.1

insert query update delete getmore command flushes mapped vsize res locked % idx miss % qr|qw ar|aw netIn netOut conn time
localhost:27017 10 0 0 0 0 0 0 464m 3.35g 5m 0.3 0 0|0 0|0 817b 787b 8 11:54:24

The work-around is to poll only one host at a time, or poll multiple hosts with no delay. (In the second case, the division will still occur, but it will be by 1.)