Over-learn the anchors and doomsday dates, always count from the month's doomsday, and self-check with a known date.

• Automate the tables — century anchors and the 12 doomsday dates must be instant, or the method stalls.
• Count from the month's own doomsday date, so offsets stay under 7 (and can be negative).
• Sanity-check against a date you know (your own birthday) to catch a slip.
• Practise daily with random dates — speed is pure repetition, and sub-10-second times are a realistic goal.

Wednesday.

1. Anchor (2000s) = Tuesday (2).
2. Year 01: q = 0, r = 1, s = 0 → 2 + 0 + 1 + 0 = 3 = Wednesday (year's doomsday).
3. The date: August's doomsday is 8/8 (Wednesday). 15 − 8 = 7, 7 mod 7 = 0 → 15 August is also Wednesday.

Check: 15 August 2001 was a Wednesday. ✓ Notice step 3 stays tiny because you count from the month's own doomsday date, never from the 1st.