Vacuum Decay (Blank-Off) Test
The evacuation standing-decay verdict: from the micron level at valve-off, the level after a timed hold, and the hold time, the total rise and the rise rate, with a tight-and-dry / moisture / leak reading against an editable 500-micron pass ceiling (ACCA Standard 4 / AHRI field practice).
Formula and source
rise_micron = end_micron - start_micron; rate_micron_per_min = rise / hold_min. Verdict: end at or below the pass ceiling (default 500 microns) is tight and dry; above it is residual moisture/outgassing if it plateaus or a leak if it climbs steadily.
First-principles standing-decay (blank-off) arithmetic (public); the 500-micron evacuation target and valve-off decay test are the common HVAC field convention (ACCA Standard 4 / AHRI / equipment manual, by name).
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