OPEN METHODS / REPRODUCIBLE EXAMPLE
Why one door-bottom gap number can hide uneven clearance
Four controlled, explicitly fictional three-point scenarios show why minimum, maximum and range matter before selecting a door sweep.
Research type: mathematical demonstration using invented inputs. Published: 2026-11-04. Version: 1.0. Field samples: 0. Product tests: 0. This is not a measured survey of door faults, a lab experiment or a quantified prediction of air leakage.
Question and method
Can three different gaps have the same arithmetic mean, yet describe different clearance shapes? We chose four scenarios, recording hypothetical gap measurements at hinge, center and latch positions on a closed door, relative to the same theoretical threshold plane. All lengths are inches.
Equations: gmin = min(g1, g2, g3); gmax = max(g1, g2, g3); variation = gmax − gmin; arithmetic mean = (g1 + g2 + g3) / 3. These descriptive values do not establish a sweep manufacturer’s clearance range.
Complete illustrative dataset
| Scenario | Hinge (in) | Center (in) | Latch (in) | Minimum | Maximum | Range | Mean |
|---|---|---|---|---|---|---|---|
| A: even | 0.2500 | 0.2500 | 0.2500 | 0.2500 | 0.2500 | 0.0000 | 0.2500 |
| B: gradual slope | 0.1875 | 0.2500 | 0.3125 | 0.1875 | 0.3125 | 0.1250 | 0.2500 |
| C: center high spot | 0.1875 | 0.3750 | 0.1875 | 0.1875 | 0.3750 | 0.1875 | 0.2500 |
| D: center low spot | 0.3125 | 0.1250 | 0.3125 | 0.1250 | 0.3125 | 0.1875 | 0.2500 |
Download the complete illustrative dataset (CSV). Inputs, outputs and units are included. Values are recorded to six decimal places in the CSV to make exact fractional results reproducible.
What the controlled examples demonstrate
All four examples have mean clearance 0.25 in. The uniform case has range 0, but the uneven cases have ranges of 0.125 or 0.1875 in. An identical mean cannot identify whether the smaller gap occurs at a door edge or the center. A sweep chosen from one average measurement could drag in a tight area and fail to touch in a larger area. These examples illustrate geometry only, not the probability or severity of either problem.
Reproduce the method
- Use the four rows in the CSV as three input gaps each.
- For each row, calculate the minimum and maximum of the three readings.
- Subtract minimum from maximum, then sum the readings and divide by 3.
- Compare the means with the ranges and note the location of the smallest gap.
- Repeat with your own three real readings using the door bottom gap checker; record threshold condition and hardware separately.
Evidence, safety and scope
The U.S. Department of Energy’s exterior-door weatherstripping instructions advise correcting door alignment and hardware problems and ensuring the seal does not prevent proper operation. See DOE job aid, June 2024 and DOE detailed job aids.
Limitations: only three locations are sampled. Actual thresholds can be irregular; readings can be affected by tape accuracy, door movement, carpet, seasonal changes and different measuring planes. This document does not test air leakage, certify a sweep working range, establish a universal tolerance or authorize alteration of fire-rated, egress or other safety-critical doors. Follow the exact door and sweep manufacturer instructions.
Attribution and corrections
Prepared by MendNook Editorial as a documented arithmetic exercise. Named editorial responsibilities are described on the About page; no member of the team is represented as having measured these fictional scenarios in a home. See all calculator equations, editorial policy, and corrections process. Permission requests: contact@mendnook.com.