Being in the SEO space, I must admit that one of the most trying things to deal with is the ever changing order of search results. More so than in years past, on highly competitive terms, we see daily and sometimes hourly fluctuations of the SERP’s and the positioning of businesses within the Google results.
Clients ask why this happens and the short answer is that Google has approximately 36 different data centers that serve as search indexes for their website traffic. Depending on time of day, geo location, and other factors that are not well known, your results for a search query will probably be different than mine. Do a search for “mortgage rates” and you will see a different mix each and every day. This is partially driven from the dynamic nature of the term, the competitive factors relating to the term, as well as the different data centers across the country and the globe.
If you are dying to see your position across all centers, there are tools to do so. I recommend not to get to caught up, however, and just concentrate on the broader metrics instead of one holy grail term.