chart caller

noun

horse racing

: a person who observes and records on charts the positions of and distances between horses at various stages of a horse race and provides analysis for these observations

He beat King of the Roxy … and Longley, who got in trouble and may have been the best horse in the race. The strong handling by Edgar Prado was duly noted by the chart caller.—

Bill Handleman, Asbury Park Press, 3 Aug. 2007

The job of a chart caller is at turns art and science. Charts and, by extension, past performances, carry the aura of inviolability, but at heart they are the interpretations and approximations of an individual. Through their binoculars, chart callers supply the information that makes up the charts on which past performances are based. These materials … are the bedrock of the whole betting structure; the actions of bettors, breeders, jockeys, trainers, even the historical veracity of the game, all depend on accurate charts.—

Ryan Goldberg, Daily Racing Form, 8 Aug. 2013