cron - Crontab timing working not as expected -

i have backup script syncing files every 3rd day.

# m    h   dom  mon  dow   0    5   */3    *    *     backup      /home/backup/scripts/system_backup.sh

today checking backup , there none.

i expected, because today 27th, 27 / 3 number, execute.

the timestamps of other backups contain days 19, 22, 25

shouldn't execute on days 18, 21, 24, 27 ?

a timestamp of server right fri jun 27 08:52:00 utc 2014.

from man page crontab(5):

step values can used in conjunction ranges. following range ``/'' specifies skips of number's value through range.

basically, means values used @ 0-based indexes divisible <number>.

for dom, * same 1-31. */3 1-31/3. means it'll start @ 1 (index 0) add 3 next 1 (4, @ index 3) , on.

if want cron run on days divisible three, can use 3-31/3 instead.

My