anchor

Chapter I defines it together with the clock: an anchored observer is a pair $(p,L)$ of a clock $p$ and a line $L$ of the Fano plane missing $p$, and $L$, one of the clock’s four reports, is its anchor. Chapter V reads the same choice on the kernel graph. Standing on one report breaks the report group from $S_4$ to the stabilizer $S_3$ of that report, and the six letters split three and three: the anchor’s rods, one on each axis, and the odd letters opposite them. Standing on $v$ and re-anchoring to $w$ moves the vantage along the letter $vw$, so a history of re-anchorings is a walk on $K_4$. The reports are places, none of them an origin, and only a vantage makes a report an origin.

Chapter II says what the choice buys. The apparatus of the selection theorem has four decoders, one for each report it could stand on, and their uniform average returns only the normalized trace of the decoded block. An observer spread evenly over its possible anchors recovers nothing of its report qubit but the trace: to see anything it must stand somewhere.