The foolproof fixture at Fuji-Xerox fits in this category. Another category is redundancy. Many companies use multi-identity codings, redundant actions or multiple tests to reduce the chance of error. For example, a number can be both read from a barcode and entered from a printed label, and only if both numbers match in the computer is the number accepted. In information quality systems, data are often entered independently by two different operators, and an automated verification system identifies any discrepancies.
Countdowns represent another category.
Checklists are actively used to ensure that every step is accomplished. Spacecraft launches are visible examples of the use of countdowns. A fourth category of foolproofing methods covers special checking and control devices. One familiar example is the automated credit card checking done by many e-commerce sites during ordering. Invalid numbers are not accepted, and feedback is given instantly.