Guilliman had been hoping to find a solution to the Imperium's tortured dating system; he had instead found there was none.
Even as he made war, the Primarch attempted to grasp the events of the ten millennia that had passed since he had fallen during the Battle of Thessala to the Daemon Primarch Fulgrim.
He was dismayed to find that much of humanity's history had fallen afoul of superstition, fanaticism and hearsay during his absence.
The check number refers to the accuracy of a given date, which is required for clarity due to the common distortions of subjective linear time that occur while travelling within the Warp, and inaccuracies in timing on remote or isolated Imperial worlds and star systems.
Check numbers are listed using the following numeric classes: For record-keeping, each year is divided into 1000 equal parts, numbered 001-000, rather than months or weeks.
The problem faced by Guilliman was that after the opening of the Great Rift, near every active Imperial war zone had to devise and reinforce its own chronological system.