How does Google measure page position in Webmasters?

[CostumeD]

Does anyone know exactly how Google measures page position in Webmaster Tools?

For example: In Google Webmaster Tools, we had a product which on the 22/12/15 was at position 7, and then dropped to position 112 on the 30/12/15. It then rose back up to position 7 on the 6/01/16 and then down to position 25 on the 16/01/16.

What does this mean and why?

[MattRoney]

Hi Li! Did Peter answer your question? If he did, please mark one or both of his responses as a "Good Answer."

[Mobilio]

Page position is volatile as i can see. You need to select page and switch to query. This will return all keywords that was shown and clicks are performed for THAT url. If you select single query you can see dance for that keyword position in SERP. I make 2 screenshots with obfuscated keywords and url where you can see this. You can look them on attachment. If you wish you can digg inside grouping traffic by device (mobile/tablet/desktop) and by country.

So dancing up and down is normal. Because Google make changes each day, they releasing new algos. Also your site getting links, social signals, etc. BUT meanwhile your competitors in SERP do same. And you playing against 100 or 1000 for some keywords.

If you look Algo change history then you can see that starting from Jan a new algo has been released as "core update". No additional information was given and it shake well SERP. Probably your up/down movements are caused from it. At this time no one can give you advice what to do except "write great content and they will follow" plus "follow guidelines". You can follow SEO experts in Twitter, Facebook and G+ because they can share interesting about it. Like:
https://twitter.com/dr_pete
https://twitter.com/CyrusShepard
https://twitter.com/randfis

4AlbM

[CostumeD]

Hi

Thanks for your answer.

The positions we are looking at are all showing in the graph for a particular product. Using the page position.

22/12 8.5

3/1 50

5/1 8

12/1 7

13/1 2

14/1 11

Can you or anyone explain why this rank varies so much day by day.

[Mobilio]

Search Analytics is only one way to check what position is your keywords and/or pages for specific queries.

There are two ways for aggregating - per site or per page. They are described here:
https://support.google.com/webmasters/answer/6155685

In first site when we have site that on one page return 3 pages on position 1,2,3 and user click somewhere - CTR = 100% because we have one click to site and average position = 1 because is calculated from highest position.
In second way (per page) - CTR = 33% (3 results and one click) and average will be 2 (1+2+3)/3 = 2.

Now going back to your questions. It's normal your positions to goes up or down. Google was making changes to their algorightms - over 400-500 per year. Some of them can be seen, other was unseen. There are few ways to be informed for changes:
http://mozcast.com/  <- this is something as weather report for Google. There are sunny days and rainy too.
https://moz.com/google-algorithm-change <- this is one of lists with changes. Some of them are confirmed, other doesnt.
Watching SEO community - can be in Twitter, Facebook, G+
Reading SEO news sites

Now back on your question. I believe that your site was going up and down from updates on 6 Jan and 16 Jan (they are confirmed as Core update). But i don't know about updates on 22 Dec or 30 Dec. Since "core update" is still in analysis of many industry leaders SEOs (even in Moz) i can't give you advise about it.