Operating profit rate
liquidation value
Stability of profit growth: If a company's profit declines in one year, it may not matter. But if you don't perform well for two years in a row, you must be skeptical.
Flexibility is the core rule: when everything goes well, you must be ready to make changes. When the whole cycle is completely in line with your forecast, you should be ready to make a profit.
Don't trust any principles and formulas: any theorem can be broken overnight.