Kinds of checking procedures
| Second check performed by | First check performed by | |
| One person | A pair of persons | |
| The same person | Double check by a single person | Double check by a pair of persons and one person |
| Another person | Double check by two single persons | Double check by a pair of persons and one single person |
| The same pair | Double check by one person and one pair of persons | Double check by a pair of persons |
| Different pair | Double check by one single person and a pair of persons | Double check by two pairs of persons |