What counting criterion is described for the Walton-Beckett Graticule?

• A. 7 f/cc or 5 fibers in 100 fields
• B. 10 f/cc or 2 fibers in 50 fields
• C. 100 f/mm^2
• D. 385 mm^2

Answer: (A)

In this counting method, you assess when a sample has enough data to give a reliable fiber concentration. The Walton-Beckett graticule uses two stopping criteria to balance speed and accuracy: you either stop once the estimated concentration reaches seven fibers per cubic centimeter, or, if that concentration isn’t reached quickly, you continue counting across fields until you’ve observed five fibers in one hundred fields. The f/cc unit means fibers per cubic centimeter of air, so counting fibers on the graticule’s fields is translated into a concentration using the known sampled air volume and the graticule’s field area. If you hit seven f/cc, you have a criterion to report confidently; if not, you keep counting up to the total of one hundred fields to achieve a minimum count (five fibers) for a more reliable estimate. The other options describe counts per area or different numeric values that do not reflect this standard stopping rule for the Walton-Beckett graticule.