Summarizing Data Using Timer

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Hi,

As part of my project, I need to collect data each d(t) time and apply some statistics methods. So, I thought to use "rospy.Timer(period, callback, oneshot=False)" function to do it - http://wiki.ros.org/rospy/Overview/Time . 'period' will be d(t) and 'callback' function will calculate statistics.

But I have a question - if my 'call_back' function takes 2 secs to run, and my period is 1 sec, how is it synchronized?

If you have another suggestions how to implement this, please offer me.