Normal sudoku rules apply. Shade each cell in the grid using one of two colours, such that all cells with the same colour are orthogonally connected, and no 2x2 square of cells is entirely one colour. Black dots between cells indicate that their digits are in a 1:2 ratio. The digits along a red arrow sum to the digit in its circle. The yin-yang colour boundary (when discovered) splits the line into segments, each of which is a separate Thermo line, all running in the same direction. Put another way, digits on this line increase continuously from the bulb, unless the line crosses a colour boundary, in which case the digit after the boundary may be lower than the one before it. All segments are either 3, 4 or 5 cells long.
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