Changes to lookup code/symbols on the NASDAQ? I'm not entirely sure if I've asked the right question, but does anyone know why certain symbols (I assume they are the symbols) change on NASDAQ?

In particular I'm wanting to keep a track of the Natural Gas price. It's current code is NGH16.NYM and I've been following it here http://finance.yahoo.com/q?s=NGH16.NYM&amp;ql=0

However last month the code was NGG16.NYM and had this URL http://finance.yahoo.com/q?s=NGG16.NYM&amp;ql=0

I've been struggling with this for a while now, and at first thought it was an incremental code. That pattern didn't seem to stick.

Any ideas? And any idea if I can predict the next ones?

Thanks :)
You are tracking futures on natural gas. Therefore, the name changes because you look at contracts with different maturities: the first has a maturity in March 2016, whereas the second that you mention is due to expire next month (February 2016).

Future contracts are derivative which reflect accurately the expectations of market participants at a defined maturity. You should try to track indexes instead of futures if you want to track commodity prices without changing the tickers and without looking too much at expectations.