The full-length paper analyzes bit stick/slip motion by coupling rock mechanics with field bottomhole data collected by use of an instrumented polycrystalline-diamond-compact (PDC) bit, a new tool that measures acceleration, weight on bit (WOB), and torque on bit (TOB) directly above the bit, Tests were conducted in Montrose, Scotland at approximately 700 m in a consolidated Devonian sandstone. The effect of stick/slip on rate of penetration (ROP) was quantified, Generally, an increase in WOE makes the system move toward stick/slip mode.