A Luo Pan is known as the Feng Shui compass. It comprises of 2 parts:
The compass is in the centre of a rotatable plate.
A plate has a “cheat sheet” or formulae laid out in a circular format around the compass.
It certainly looks impressive, but it can be heavy to carry over a long period of time. To use it properly, you are to be shown by a teacher to hold it, align it with the object you measure against.
After the measurement, you look at the formulae in the circles for the analysis.
I prefer to use a proper western compass with a print overlay of the main eight directions and the 24 mountains.
The diameter of the compass component of the Luo Pan is 3.0 cm. The western compass is larger at 3.5cm. The main difference is the western compass needle movement is dampened, so the needle movement is more stable and easier to read. It is also small, convenient and discreet.
The marking in the inner ring is the cheat sheet for 8 trigrams and 24 mountains sectors.