Claudius's ability is visual/neural - when activated, he can locate and identify patterns of all kinds. If placed in front of raw data, he can distill the unifying trends and principles guiding that data. This does not mean, however, that he can always determine the significance of those trends. That requires actual analysis. Also, the sheer number of possible patterns makes his ability unwieldy, so it helps if he has an understanding of what he is trying to discern, has some preliminary context or conscious filter.
The ability is on/off, and when activated, his eyes change pigmentation, turning a bright yellow. After many years of practice, Kellar no longer turns his ability off and constantly possesses unnaturally-colored eyes. While active, the ability's reception is partially passive - it will latch on to any pattern he sees, unless he guides it. It is no longer exhausting for Kellar to use his ability, and he has become adept at rapidly recognizing patterns.
The applications of his ability are various, though rarely of any significant value unless he has trained them. Seeing patterns without focus leads one to total cognitive chaos, so he uses learned knowledge and concentration to focus on useful patterns. He is able to process massive amounts information, but on an intuitive 'blink' level that never makes its way into long term memory in detail (only the pattern sinks in that way), so he can only use his ability on material he can either return to later, or recall in short term memory. E.g. if assigned to examine currency future trends within Balkan countries to determine which ones should be hedged against each other, he would need a.) knowledge of how to perform arbitrage and b.) files detailing the currency trends of the various countries. That way he could examine all the information at leisure, going back to 'refresh' himself, and he would be able to look for the trends relevant to predicting profitable arbitrage investments.
Within his life, he has studied patterns and puzzles, to hone his ability, so he's a mean shake at a lot of pattern based games, is a fairly skillful amateur code breaker, and can often improvise techniques that lead to educated pattern 'guessing' - he could give a solid crack, having learned just a bit about generational genetics (particularly after reading Activating Evolution), at noticing patterns of shared characteristics and thus theorize whether or not certain people are related just by looking at them with his ability active.
Note, his ability can make him draw the wrong conclusions if he's a.) using the wrong information (e.g. if he misremembered a fact about generational genetics) b.) is misled somehow (the people are disguised to appear like family, with contact lenses and wigs), c.) he is forced to fill in an interpretation because he can't interpret it otherwise (all of them are wearing glasses so he 'fills in' the conclusion where they are all hereditary myopics, even if that's not the actual condition they have) or d.) forgets to filter a pattern that is irrelevant (they all are wearing the same color somewhere in their clothing). This last kind of wrong conclusion is precisely what aggravates and his paranoia.
His ability also has side effects, due to prolonged use. Headaches and eye strain are to be expected, and most definitely occur. However, much more dangerous is the paranoia that emerges, an augmentation of his already present personality style. For lack of a pattern to see, his brain will force a pattern onto what he sees, making cognitive leaps and linking things that have no actual link. This process, definitionally paranoid, latches onto his already present fears of persecution and fill him with a nameless dread.
