Armstrong, who has refereed at all three Football League levels this season, taking charge of 22 games, has a steady but not overboard crime count.
Having issued five yellow cards in a game on two occasions, he totals 55 yellows, with four players on the receiving end of reds and sent for an early bath.
On Saturday his assistants are R T Hewitt and M Oliver.
The fourth official is Mr D K Benton.
Head to head and team news will be online tomorrow, as the news of Knill's departure digests.