How are rankings of keywords calculated?
Sellics only tracks the keyword rankings within all categories.
Rankings within specific categories are not tracked.
How often are rankings of keywords updated?
For all tracked keywords, the rankings will be crawled daily over night (of the respective marketplace) for all your added ASINs. As a result there may be certain ranking shifts in the meantime from what is shown in Sellics.
Beware of Algorithm Tests & Personalized Search results (Clear Cache)
Finally, keep in mind Amazon is constantly trying to improve the customer experience and thus search algorithm, which may lead to temporary ranking shifts. Personalized search results are also being worked on, so it may be necessary to clear the browser's cache (hold Ctrl + Shift + R) or activate Inkognito Mode to see the actual non-personalized search results.
For more information on how Organic Ranking works, visit What is Organic Ranking? How do I track my keywords?