A common framed primitive meridian

Choose the collar basepoint

in sector zero. Use the reference affine chart there, without re-centring its origin.

A collar meridian is the polygonal loop $\rho =15/4$, based at $b_s$, traversed in increasing angular order. In the collar face charts its ordered word is

and therefore its affine product is exactly $J$.

For a loop strictly inside the moving core, choose

Because

this loop lies in the $V_i$ faces for every $s\in [-1,1]$. Join it to $b_s$ along the bisector of sector zero. The resulting based meridian is denoted ${\gamma }_s$.