discrepancy in stock volume amounts at Yahoo, Google, Stock Market Watch etc.

I have a question regarding differing stock volume amounts for a specific stock reported on various financial websites. For example, let's take a look at Lockheed Martin's volume amount at 12-12-2016.

Yahoo Finance: 7 080 300
https://finance.yahoo.com/quote/LMT...83600&interval=1d&filter=history&frequency=1d

Google Finance: 7 080 271
https://www.google.com/finance/hist...e=Dec+13,+2016&num=30&ei=wrWEWIGdIMWCswHOr4No

Stock Market Watch: 7 079 560
http://thestockmarketwatch.com/stoc...endDay=12&endYear=2016&endDateLite=01/22/2017

and finally the Lockheed Martin's official website: 7 078 760
http://phx.corporate-ir.net/phoenix...Lookup&t=HistQuote&control_firstdatereturned=

My guess is that it perhaps could be a result of some data providers including pre-market and after-hours trading into the calculation of the volume but still, 4 different numbers?

I hope someone can explain this. Thank you in advance.

Does really no one know the answer?

Depends on the data provider. Various sources. Slight diff shouldn't be s concern.

Check nse site.

Lockheed Martin is not listed in NSE.

Also after-hours trading concept doesn't exist in NSE as well.

Bhai logon,
he is talking about a scrip listed at Wall Street and not NSE.

In india, we have a after hours market, 3:50 - 4:00. Stocks trade at fixed price.

What is duration for their after hours. Does the price change?