Chronometric data
From Memory Alpha, the free Star Trek reference.
Chronometric data was the data collected by the 29th century timeship Aeon.
The temporal sensors on board worked in the way normal ship sensors would scan space. They scanned temporal anomalies in the space-time continuum and collected data on it. This data was fed into the computer and was compared to the known "Normal" timeline. (VOY: "Future's End", "Future's End, Part II")
