Price to Book ratio and PE ratio

My rule of thumb for P/B ratio is:

• P/B less than 2 implies chances of undervaluation
  
• P/B between 2 and 3 indicates possible fair valuation
• P/B more than 3 probably indicates over valuation, anything above 5 possibly means grossly overvalued
  

My rule of thumb for P/E ratio is:

• P/E less than 10 implies chances of undervaluation
  
• P/E between 10 and 20 indicates possible fair valuation
• P/B more than 20 probably indicates over valuation, anything above 50 possibly means grossly overvalued