Feng Shui Luopan 羅盤 , regardless of their different sizes, can be classified into 2 or 3 types:
 
1) sam he luopan 三合盤
2) sam yuen luopan 三元盤
3) sam yuen and sam he combined luopan 三元三合混合盤
 
Sam yuen luopan is commonly used nowadays, mainly by sam yuen flying star and trigram stream practitioners. Sam he luopan is rarely used nowadays except for few old masters still expertise in the sam he stream.
In fact, sam he stream and its luopan has a far longer history in fengshui than the sam yuen. Sam yuen stream and its luopan were made known in fengshui history only since late ming dynasty to early ching dynasty onwards in china.
 
How to differentiate sam he luopan from sam yuen luopan?
 
There are 2 simple ways so, doing with the design of 24 mountains
 
  1. sam he luopan has 3 layers (heaven, earth, human) of 24 mountains, whereas a pure sam yuen luopan has only 1 layer (earth) of 24 mountains
  2. sam he luopan has 24 mountains in red (yang) and black (yin) color but locates not evenly (not 3 red follows by 3 black constantly). A pure sam yuen luopan has 24 mountains with yang and yin color in sequence of 3 red and 3 black evenly.
This is due to sam he and sam yuen are having differnt theories and methods for classification of the 24 mountains into yin and yang.