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Transit timing variations (TTVs) of binary stars and extra-solar planets are easily measured and reveal information about such star systems. Transits are revealed by light curves showing a periodic dip with a very consistent period, but the period can be very slightly altered by the gravity of a third body, and these slight alterations in the period are the TTVs, which can be analyzed, revealing the presence of additional stars, planets, and/or exosatellites (TTV method). They can also reveal information on masses, in particular ratios of masses; determination of actual masses (or masses relative to the host star) likely requires modeling and computation. Transits varying in an anti-correlated manner, i.e., one occurring sooner and another later, provide evidence of an additional planet because this behavior is typical when two planets are affecting each other's orbits.
Transit duration variations (TDVs) are also used for analyzing possible three-body systems.