The ribbon that spirals around the oval is a single continuous twist, and getting it to close is a piece of arithmetic done before any carving starts.
A twist has a pitch - the distance along the frame that one full turn occupies. Set the pitch by eye and the ribbon will arrive back at its starting point mid-turn, leaving a visible stutter where the two ends meet. So our artisans measure the full length of the oval's centre line first, divide it by a whole number of turns, and use the result as the pitch. The twist then closes on itself exactly.
Because the oval's curvature changes - tight at the ends, flat along the flanks - the ribbon is also made slightly wider where the curve is tightest, so the width appears constant to a viewer standing in front of it.
The join is placed at the bottom of the oval, under the flower swag, which is where nobody looks. Everything else about the twist is designed to be looked at.