Through dynamic simulation of the cross-hinge four-bar mechanism. it is found the primary reason for unbalance of the mechanism results from the unequal swing angle of driving link and driven link. To simplify analysis and calculation. a spatial switching approach was proposed to switch nonlinear problem into linear problem. https://www.roneverhart.com/Apple-Watch-Ultra-2-GPS-Cellular-49mm-Titanium-Case-with-Blue-Black-Trail-Loop-S-M-MRF53LL-A/