Which description best explains how to determine the day-to-day shift?

• A. Add today's count to the previous four counts and take their average.
• B. Find the average of the previous four counts, calculate the difference with today's count, divide by the average, multiply by 100, and do this for both density and moisture counts separately.
• C. Use only today's count without considering prior readings.
• D. Compute a standard deviation and compare to a fixed threshold.

Answer: (B)

Understanding day-to-day shift means gauging how today's compaction readings compare to recent history. The method uses the average of the last four readings as a baseline, then subtracts that baseline from today’s reading, divides by the baseline, and multiplies by 100 to express it as a percent change. Doing this separately for density and moisture captures shifts in both properties, since they can move differently and both affect compaction quality. This approach provides a clear measure of whether the current day’s results are improving or declining relative to the recent trend, rather than relying on raw values that can be noisy or biased if today is included in the baseline. The other options either blend today into the baseline, ignore history, or measure overall variability without tying it to recent trend.