Information from Baidu Encyclopedia, 304 stainless steel is a commonly used stainless steel material, commonly used in the production of kitchen utensils, cutlery, medical equipment and so on. "Detecting content plus or minus 3a" refers to the margin of error used when testing the content of an element in 304 stainless steel.
The "A" indicates the percentage of elemental content, and the "plus or minus 3" indicates the range of detection error, i.e., the actual elemental content is within plus or minus 3% of the detection result, which is considered to be in line with the standard. Therefore, if a 304 stainless steel material of a certain element content standard for 10A, then its test results between 9.7A ~ 10.3A are considered qualified.