Canon EOS-1D X Mark III EOS-1DX Mark III Advanced User Guide - Page 384

Initial Servo AF pt, / You can set the initial AF point for AI Servo AF/Servo AF when the AF area selection mode is set to [Auto selection AF], or when the AF method is set to [ +Tracking]. : Auto The initial AF point for AI Servo AF/Servo AF is set automatically to suit the shooting conditions. [ ] Initial AF pt set for / AI Servo AF/Servo AF starts from the manually selected AF point when the AF area selection mode is set to [Auto selection AF], or when the AF method is set to [ +Tracking]. [ ] AF pt set for AI Servo AF/Servo AF starts from the AF point that was set manually before switching from Spot AF, 1-point AF, or AF point expansion (Manual selection ) or AF point expansion (manual selection: surround) to [Auto selection AF] or [ +Tracking]. Useful for starting AI Servo AF/Servo AF from the AF point set before switching to [Auto selection AF] or [ +Tracking]. Note When [AF pt set for ] is set, AI Servo AF/Servo AF starts from a zone corresponding to your manually selected AF point even if you switch the AF area selection mode to Zone AF or Large Zone AF, or switch the AF method to Zone AF or Large Zone AF (vertical or horizontal). 384