Tianchi, also known as the seabed, is also a compass. The Tianchi of the feng shui plate consists of a thimble, a magnetic needle, a submarine thread, a cylindrical outer box and a glass cover, which are fixed in the center of the inner plate. There is a pointed thimble in the center of the bottom surface of the round box, a concave hole in the center of the bottom surface of the magnetic needle, and the magnetic needle is placed on the thimble. The arrow of the compass points to the south and the other end points to the north. There is a red line drawn on the bottom of Tianchi Lake, which is called the seabed line. The north end is flanked by two red dots. When in use, the north end of the magnetic needle must coincide with the seabed line. The seabed of the modern feng shui tray is painted with crosshairs. When in use, the north end of the magnetic needle should point to the north end of the submarine cross, and the magnetic needle should coincide with the north-south line of the seabed.

The inner disc is the rotatable disc immediately outside the compass. There are many concentric circles printed on the inner disk, one circle is called a layer, each layer is divided into different equal parts, some layers have more grids, some layers have less grids, the least is divided into eight grids, and the layer with the most grids has Three hundred and eighty-four grids, each with a different character printed on it. There are many types of feng shui plates, some with many layers, some with few layers, the most with fifty-two layers, and the least with only five layers. The various contents of the feng shui plate are engraved on the different circles (layers) of the inner plate, which are the main components of the feng shui plate.

The outer disk is square and serves as a tray for the inner disk. There is a small hole at the midpoint of the outer sides of the four sides, which penetrates the red line to become the ten paths of Tianxin, which is used to read the contents of the inner disk. The ten principles of Tianxin are perpendicular to each other, and the newly purchased compass must be calibrated before use.