Timber Cruising Calculator

Both can move it substantially, in opposite directions. Total Sample Plot Volume is a direct multiplier, so raising it always raises the estimate. Plots Measured sits in the denominator when computing average volume per plot, so raising it — while holding the sample total fixed — lowers the estimate instead. Which one swings the result further depends on where you're starting from in each input's range. Plots Measured stops lowering the estimate once it reaches Total Plots in Stand — past that point you have censused the whole stand and the estimate is flat at your tallied volume.

No — Stand Acreage is used only to compute Volume Per Acre, a separate output. Estimated Stand Volume comes entirely from Total Sample Plot Volume and the expansion factor built from Plots Measured and Total Plots in Stand, so acreage has no effect on it, though it directly determines the per-acre figure.

It's a commonly cited rule-of-thumb figure for timber stand variability, not a number measured from your specific sample. The Standard Error and 95% confidence interval both derive from this assumed 40% CV rather than from the spread across your individual plot measurements, so treat the interval as a generic estimate of typical cruise precision, not a statistically rigorous analysis of this stand. The interval also carries the finite-population correction, so it narrows as your sampling intensity rises and collapses to zero at a 100% census.

It does not use Total Sample Plot Volume or Plots Measured, because it answers a design question rather than a results question: how many plots a stand with the assumed 40% coefficient of variation needs to hit a 10% allowable error at 95% confidence. It does respond to Total Plots in Stand, through the finite-population correction — a stand with only 50 possible plot locations needs 29 plots for that precision, while a very large stand approaches 64.