We investigated the structure-forces coevolution in rotational shear of a planar assembly of photo-elastic polyurethane-discs of four different sizes under constant confining stress [1,2]. Disc positions and contacts were determined using unpolarized red light. A dark-field polariscope, using circularly polarized blue light, detected mechanical deformations and the force network. The experiment ran through: a de-correlation step, initial state preparation, steady-state dynamics. Repeated measurements of the structure and cell order distribution of the geometric contact network were carried out, validating theoretical predictions of detailed balance[3,4] and maximum entropy[5]. Simultaneously detected force chain networks had more cells of higher orders than the geometric network, providing less than maximum entropy. This is attributed to the sensitivity of force detection to low-force contacts. Characteristic differences also existed in the shapes of small cells.