ISO 105 A03, AATCC/EP2, GB/T 251
1. Keep the gray card clean.
2. The gray card should be checked frequently for finger marks and other marks.
3. If the marks are found to have interfered with the rating, the card must be replaced.
4. Avoid mechanical damage from touching.
5. If mechanical damage interferes with the rating, it should be replaced.
6. When the gray card is used up, put it into the sleeve.