Converting JMeter Timestamp

Sometimes, I forget to configure JMeter so that the timestamps in the JTL are human readable.  Instead, I could end up with a results file that looks like this:

---

timeStamp,elapsed,label,responseCode,responseMessage, ...
1486489879434,211,HTTP Request,204,No Content,...

---

The timestamp displayed is in "epoch" time.  The only caveat is that this timestamp is in milliseconds.  So, in order to convert it you would need to do the following:

1. Divide the time stamp to get the time in seconds
2. Divide by the total number of seconds ind a day (60 * 60 *24)
3. Add to the number of days since January 1, 1970

Luckily, many programming languages have a library that handle that.  In the case of ruby, 

require 'date'

​timestamp = 1486489879434
puts Time.at(timestamp/1000)

which returns '2017-02-07 09:51:18 -0800'