How do you know whether edible oil is healthy or not?

Generally, there will be no problem if it passes the national sampling inspection. Because oil will appear different colors after repeated frying, the more frying times, the darker the color. The fourth time, it was dark red. Or the acidity can be measured, and ATAGO DOM-24 can detect the TPM value of the engine oil, so as to judge whether the engine oil has deteriorated.