A pressing device for a pen and the pen further comprises a spring, and a center stick fitting with the spring and having a nib part. By adding or subtracting these inputs in the compensation circuit, an output fluctuation due to temperature of the first photodiode is removed. Each frame unit includes a continuous track, enabling forward movement of the serpentine robotic crawler. The grain pieces are passed to a second heating step to reach a second elevated temperature, followed by a second cooling step.