"In effect the rock becomes a calendar or diary of events."

That would be mega-neat, but as you say it would need a specific stick length, which seems highly unlikely. I was thinking more that it simply commemorated the direction in which Albert passed during the ceremony, and any length stick would do for that. If I start claiming it marks the day and hour, and you could find his anniversary by bringing the stick back next year, I'll attract just a morsel of criticism... ;)