FAILURE MAP
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FA-92521 / HVAC thermostat control / Open access

Fahrenheit press steps from a truncated whole degree · case 01

Pressing up from a stored 72.5 F shows 73 instead of 74.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The whole-degree base floors the stored tenths.

THE FAILURE

The whole-degree base floors the stored tenths.

Unsuccessful approach: Banker's rounding still steps from 72 for a stored 72.5.

Case contract

Thermostat setpoint keypad. The setpoint is stored in tenths F. In C mode the display shows the stored value converted to C and rounded half up to 0.5 C; a press moves the displayed value by 0.5 C and stores exactly 320 + half_degrees*9 tenths F. In F mode the display rounds half up to whole F and a press moves the whole-degree value by 1 F. After each press the stored value is clamped to 45.0-90.0 F. Return [display, stored_tenths_F] per press.

Why this case matters

Residential and light-commercial thermostats make these decisions sample by sample; each defect changes equipment calls in a way that shows up as short cycling, comfort complaints or equipment stress.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(unit, presses, start_f10):
    f10 = start_f10
    out = []
    for p in presses:
        step = 1 if p == 'up' else -1
        if unit == 'C':
            c_half = (2 * (f10 - 320) + 9) // 18
            f10 = 320 + (c_half + step) * 9
        else:
            f_whole = f10 // 10
            f10 = (f_whole + step) * 10
        f10 = max(450, min(900, f10))
        if unit == 'C':
            c_half = (2 * (f10 - 320) + 9) // 18
            out.append(['%d.%d' % (c_half // 2, 5 * (c_half % 2)), f10])
        else:
            out.append([str((f10 + 5) // 10), f10])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: fahrenheit half value',
   ['F', ['up', 'down', 'down'], 725],
   [['74', 740], ['73', 730], ['72', 720]]],
  ['regression: scenario 7',
   ['F', ['down', 'up', 'down', 'up'], 905],
   [['90', 900], ['90', 900], ['89', 890], ['90', 900]]],
  ['control: celsius steps', ['C', ['up', 'up', 'down'], 720], [['22.5', 725], ['23.0', 734], ['22.5', 725]]],
  ['control: upper clamp', ['F', ['up'], 895], [['90', 900]]],
  ['control: celsius off-grid start', ['C', ['down', 'up'], 716], [['21.5', 707], ['22.0', 716]]],
  ['control: celsius lower clamp',
   ['C', ['down', 'down', 'up'], 452],
   [['7.0', 450], ['7.0', 450], ['7.5', 455]]],
  ['control: celsius half-step display', ['C', ['up'], 707], [['22.0', 716]]],
  ['regression: scenario 1',
   ['F', ['down', 'down', 'up', 'up', 'up', 'down', 'down', 'up'], 716],
   [['71', 710], ['70', 700], ['71', 710], ['72', 720], ['73', 730], ['72', 720], ['71', 710], ['72', 720]]]],
 [['regression: scenario 2',
   ['F', ['down', 'down', 'up', 'down', 'up', 'down', 'up', 'up'], 725],
   [['72', 720], ['71', 710], ['72', 720], ['71', 710], ['72', 720], ['71', 710], ['72', 720], ['73', 730]]],
  ['regression: scenario 3',
   ['F', ['down', 'up', 'up', 'up', 'up', 'down', 'up', 'down', 'up'], 725],
   [['72', 720],
    ['73', 730],
    ['74', 740],
    ['75', 750],
    ['76', 760],
    ['75', 750],
    ['76', 760],
    ['75', 750],
    ['76', 760]]],
  ['control: celsius steps', ['C', ['up', 'up', 'down'], 720], [['22.5', 725], ['23.0', 734], ['22.5', 725]]],
  ['regression: fahrenheit half value',
   ['F', ['up', 'down', 'down'], 725],
   [['74', 740], ['73', 730], ['72', 720]]],
  ['control: upper clamp', ['F', ['up'], 895], [['90', 900]]],
  ['control: celsius off-grid start', ['C', ['down', 'up'], 716], [['21.5', 707], ['22.0', 716]]],
  ['control: celsius lower clamp',
   ['C', ['down', 'down', 'up'], 452],
   [['7.0', 450], ['7.0', 450], ['7.5', 455]]],
  ['control: celsius half-step display', ['C', ['up'], 707], [['22.0', 716]]]],
 [['regression: scenario 3',
   ['F', ['down', 'down', 'up', 'up', 'up', 'up', 'down', 'up', 'down'], 725],
   [['72', 720],
    ['71', 710],
    ['72', 720],
    ['73', 730],
    ['74', 740],
    ['75', 750],
    ['74', 740],
    ['75', 750],
    ['74', 740]]],
  ['regression: scenario 14',
   ['F', ['up', 'up', 'down', 'up', 'up', 'down'], 725],
   [['74', 740], ['75', 750], ['74', 740], ['75', 750], ['76', 760], ['75', 750]]],
  ['control: celsius steps', ['C', ['up', 'up', 'down'], 720], [['22.5', 725], ['23.0', 734], ['22.5', 725]]],
  ['regression: fahrenheit half value',
   ['F', ['up', 'down', 'down'], 725],
   [['74', 740], ['73', 730], ['72', 720]]],
  ['control: upper clamp', ['F', ['up'], 895], [['90', 900]]],
  ['control: celsius off-grid start', ['C', ['down', 'up'], 716], [['21.5', 707], ['22.0', 716]]],
  ['control: celsius lower clamp',
   ['C', ['down', 'down', 'up'], 452],
   [['7.0', 450], ['7.0', 450], ['7.5', 455]]],
  ['control: celsius half-step display', ['C', ['up'], 707], [['22.0', 716]]]],
 [['regression: scenario 3',
   ['F', ['down', 'down', 'down', 'up', 'down', 'up'], 716],
   [['71', 710], ['70', 700], ['69', 690], ['70', 700], ['69', 690], ['70', 700]]],
  ['regression: scenario 14',
   ['F', ['down', 'down', 'up', 'down', 'down', 'down', 'up', 'down', 'down'], 905],
   [['90', 900],
    ['89', 890],
    ['90', 900],
    ['89', 890],
    ['88', 880],
    ['87', 870],
    ['88', 880],
    ['87', 870],
    ['86', 860]]],
  ['control: celsius steps', ['C', ['up', 'up', 'down'], 720], [['22.5', 725], ['23.0', 734], ['22.5', 725]]],
  ['regression: fahrenheit half value',
   ['F', ['up', 'down', 'down'], 725],
   [['74', 740], ['73', 730], ['72', 720]]],
  ['control: upper clamp', ['F', ['up'], 895], [['90', 900]]],
  ['control: celsius off-grid start', ['C', ['down', 'up'], 716], [['21.5', 707], ['22.0', 716]]],
  ['control: celsius lower clamp',
   ['C', ['down', 'down', 'up'], 452],
   [['7.0', 450], ['7.0', 450], ['7.5', 455]]],
  ['control: celsius half-step display', ['C', ['up'], 707], [['22.0', 716]]]],
 [['regression: scenario 5',
   ['F', ['down', 'up', 'down', 'up', 'up', 'up'], 905],
   [['90', 900], ['90', 900], ['89', 890], ['90', 900], ['90', 900], ['90', 900]]],
  ['regression: scenario 43',
   ['F', ['up', 'up', 'down', 'up', 'up', 'down', 'down', 'down'], 725],
   [['74', 740], ['75', 750], ['74', 740], ['75', 750], ['76', 760], ['75', 750], ['74', 740], ['73', 730]]],
  ['control: celsius steps', ['C', ['up', 'up', 'down'], 720], [['22.5', 725], ['23.0', 734], ['22.5', 725]]],
  ['regression: fahrenheit half value',
   ['F', ['up', 'down', 'down'], 725],
   [['74', 740], ['73', 730], ['72', 720]]],
  ['control: upper clamp', ['F', ['up'], 895], [['90', 900]]],
  ['control: celsius off-grid start', ['C', ['down', 'up'], 716], [['21.5', 707], ['22.0', 716]]],
  ['control: celsius lower clamp',
   ['C', ['down', 'down', 'up'], 452],
   [['7.0', 450], ['7.0', 450], ['7.5', 455]]],
  ['control: celsius half-step display', ['C', ['up'], 707], [['22.0', 716]]]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: fahrenheit half value[['73', 730], ['72', 720], ['71', 710]][['74', 740], ['73', 730], ['72', 720]]Failed
regression: scenario 7[['89', 890], ['90', 900], ['89', 890], ['90', 900]][['90', 900], ['90', 900], ['89', 890], ['90', 900]]Failed
control: celsius steps[['22.5', 725], ['23.0', 734], ['22.5', 725]][['22.5', 725], ['23.0', 734], ['22.5', 725]]Passed
control: upper clamp[['90', 900]][['90', 900]]Passed
control: celsius off-grid start[['21.5', 707], ['22.0', 716]][['21.5', 707], ['22.0', 716]]Passed
control: celsius lower clamp[['7.0', 450], ['7.0', 450], ['7.5', 455]][['7.0', 450], ['7.0', 450], ['7.5', 455]]Passed
control: celsius half-step display[['22.0', 716]][['22.0', 716]]Passed
regression: scenario 1[['70', 700], ['69', 690], ['70', 700], ['71', 710], ['72', 720], ['71', 710], ['70', 700], ['71', 710]][['71', 710], ['70', 700], ['71', 710], ['72', 720], ['73', 730], ['72', 720], ['71', 710], ['72', 720]]Failed

SHA-256 / f58b53cae079fd84d517fd3900cea4c81ad1ce6505c1d0e7938b5bd21f6083e9

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(unit, presses, start_f10):
    f10 = start_f10
    out = []
    for p in presses:
        step = 1 if p == 'up' else -1
        if unit == 'C':
            c_half = (2 * (f10 - 320) + 9) // 18
            f10 = 320 + (c_half + step) * 9
        else:
            f_whole = round(f10 / 10)
            f10 = (f_whole + step) * 10
        f10 = max(450, min(900, f10))
        if unit == 'C':
            c_half = (2 * (f10 - 320) + 9) // 18
            out.append(['%d.%d' % (c_half // 2, 5 * (c_half % 2)), f10])
        else:
            out.append([str((f10 + 5) // 10), f10])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: fahrenheit half value',
   ['F', ['up', 'down', 'down'], 725],
   [['74', 740], ['73', 730], ['72', 720]]],
  ['regression: scenario 7',
   ['F', ['down', 'up', 'down', 'up'], 905],
   [['90', 900], ['90', 900], ['89', 890], ['90', 900]]],
  ['control: celsius steps', ['C', ['up', 'up', 'down'], 720], [['22.5', 725], ['23.0', 734], ['22.5', 725]]],
  ['control: upper clamp', ['F', ['up'], 895], [['90', 900]]],
  ['control: celsius off-grid start', ['C', ['down', 'up'], 716], [['21.5', 707], ['22.0', 716]]],
  ['control: celsius lower clamp',
   ['C', ['down', 'down', 'up'], 452],
   [['7.0', 450], ['7.0', 450], ['7.5', 455]]],
  ['control: celsius half-step display', ['C', ['up'], 707], [['22.0', 716]]],
  ['regression: scenario 1',
   ['F', ['down', 'down', 'up', 'up', 'up', 'down', 'down', 'up'], 716],
   [['71', 710], ['70', 700], ['71', 710], ['72', 720], ['73', 730], ['72', 720], ['71', 710], ['72', 720]]]],
 [['regression: scenario 2',
   ['F', ['down', 'down', 'up', 'down', 'up', 'down', 'up', 'up'], 725],
   [['72', 720], ['71', 710], ['72', 720], ['71', 710], ['72', 720], ['71', 710], ['72', 720], ['73', 730]]],
  ['regression: scenario 3',
   ['F', ['down', 'up', 'up', 'up', 'up', 'down', 'up', 'down', 'up'], 725],
   [['72', 720],
    ['73', 730],
    ['74', 740],
    ['75', 750],
    ['76', 760],
    ['75', 750],
    ['76', 760],
    ['75', 750],
    ['76', 760]]],
  ['control: celsius steps', ['C', ['up', 'up', 'down'], 720], [['22.5', 725], ['23.0', 734], ['22.5', 725]]],
  ['regression: fahrenheit half value',
   ['F', ['up', 'down', 'down'], 725],
   [['74', 740], ['73', 730], ['72', 720]]],
  ['control: upper clamp', ['F', ['up'], 895], [['90', 900]]],
  ['control: celsius off-grid start', ['C', ['down', 'up'], 716], [['21.5', 707], ['22.0', 716]]],
  ['control: celsius lower clamp',
   ['C', ['down', 'down', 'up'], 452],
   [['7.0', 450], ['7.0', 450], ['7.5', 455]]],
  ['control: celsius half-step display', ['C', ['up'], 707], [['22.0', 716]]]],
 [['regression: scenario 3',
   ['F', ['down', 'down', 'up', 'up', 'up', 'up', 'down', 'up', 'down'], 725],
   [['72', 720],
    ['71', 710],
    ['72', 720],
    ['73', 730],
    ['74', 740],
    ['75', 750],
    ['74', 740],
    ['75', 750],
    ['74', 740]]],
  ['regression: scenario 14',
   ['F', ['up', 'up', 'down', 'up', 'up', 'down'], 725],
   [['74', 740], ['75', 750], ['74', 740], ['75', 750], ['76', 760], ['75', 750]]],
  ['control: celsius steps', ['C', ['up', 'up', 'down'], 720], [['22.5', 725], ['23.0', 734], ['22.5', 725]]],
  ['regression: fahrenheit half value',
   ['F', ['up', 'down', 'down'], 725],
   [['74', 740], ['73', 730], ['72', 720]]],
  ['control: upper clamp', ['F', ['up'], 895], [['90', 900]]],
  ['control: celsius off-grid start', ['C', ['down', 'up'], 716], [['21.5', 707], ['22.0', 716]]],
  ['control: celsius lower clamp',
   ['C', ['down', 'down', 'up'], 452],
   [['7.0', 450], ['7.0', 450], ['7.5', 455]]],
  ['control: celsius half-step display', ['C', ['up'], 707], [['22.0', 716]]]],
 [['regression: scenario 3',
   ['F', ['down', 'down', 'down', 'up', 'down', 'up'], 716],
   [['71', 710], ['70', 700], ['69', 690], ['70', 700], ['69', 690], ['70', 700]]],
  ['regression: scenario 14',
   ['F', ['down', 'down', 'up', 'down', 'down', 'down', 'up', 'down', 'down'], 905],
   [['90', 900],
    ['89', 890],
    ['90', 900],
    ['89', 890],
    ['88', 880],
    ['87', 870],
    ['88', 880],
    ['87', 870],
    ['86', 860]]],
  ['control: celsius steps', ['C', ['up', 'up', 'down'], 720], [['22.5', 725], ['23.0', 734], ['22.5', 725]]],
  ['regression: fahrenheit half value',
   ['F', ['up', 'down', 'down'], 725],
   [['74', 740], ['73', 730], ['72', 720]]],
  ['control: upper clamp', ['F', ['up'], 895], [['90', 900]]],
  ['control: celsius off-grid start', ['C', ['down', 'up'], 716], [['21.5', 707], ['22.0', 716]]],
  ['control: celsius lower clamp',
   ['C', ['down', 'down', 'up'], 452],
   [['7.0', 450], ['7.0', 450], ['7.5', 455]]],
  ['control: celsius half-step display', ['C', ['up'], 707], [['22.0', 716]]]],
 [['regression: scenario 5',
   ['F', ['down', 'up', 'down', 'up', 'up', 'up'], 905],
   [['90', 900], ['90', 900], ['89', 890], ['90', 900], ['90', 900], ['90', 900]]],
  ['regression: scenario 43',
   ['F', ['up', 'up', 'down', 'up', 'up', 'down', 'down', 'down'], 725],
   [['74', 740], ['75', 750], ['74', 740], ['75', 750], ['76', 760], ['75', 750], ['74', 740], ['73', 730]]],
  ['control: celsius steps', ['C', ['up', 'up', 'down'], 720], [['22.5', 725], ['23.0', 734], ['22.5', 725]]],
  ['regression: fahrenheit half value',
   ['F', ['up', 'down', 'down'], 725],
   [['74', 740], ['73', 730], ['72', 720]]],
  ['control: upper clamp', ['F', ['up'], 895], [['90', 900]]],
  ['control: celsius off-grid start', ['C', ['down', 'up'], 716], [['21.5', 707], ['22.0', 716]]],
  ['control: celsius lower clamp',
   ['C', ['down', 'down', 'up'], 452],
   [['7.0', 450], ['7.0', 450], ['7.5', 455]]],
  ['control: celsius half-step display', ['C', ['up'], 707], [['22.0', 716]]]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: fahrenheit half value[['73', 730], ['72', 720], ['71', 710]][['74', 740], ['73', 730], ['72', 720]]Failed
regression: scenario 7[['89', 890], ['90', 900], ['89', 890], ['90', 900]][['90', 900], ['90', 900], ['89', 890], ['90', 900]]Failed
control: celsius steps[['22.5', 725], ['23.0', 734], ['22.5', 725]][['22.5', 725], ['23.0', 734], ['22.5', 725]]Passed
control: upper clamp[['90', 900]][['90', 900]]Passed
control: celsius off-grid start[['21.5', 707], ['22.0', 716]][['21.5', 707], ['22.0', 716]]Passed
control: celsius lower clamp[['7.0', 450], ['7.0', 450], ['7.5', 455]][['7.0', 450], ['7.0', 450], ['7.5', 455]]Passed
control: celsius half-step display[['22.0', 716]][['22.0', 716]]Passed
regression: scenario 1[['71', 710], ['70', 700], ['71', 710], ['72', 720], ['73', 730], ['72', 720], ['71', 710], ['72', 720]][['71', 710], ['70', 700], ['71', 710], ['72', 720], ['73', 730], ['72', 720], ['71', 710], ['72', 720]]Passed

SHA-256 / 63cdb64dbd19f72b9b3cc957586dde03e1438894c34234eb3568b8803e4be710

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The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

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Verification & scope

A deterministic bounded teaching model of one thermostat or HVAC controller decision evaluated per sample. Temperatures are integer tenths of a degree Fahrenheit unless stated otherwise. The contract is a stipulated toy convention, not a claim of conformance to any manufacturer, ASHRAE guideline or code. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:51:46.492944+00:00.

Case digest / 5af8879ea9963dd904c0d9b03f719c5b83d3a1dde15919b95c0eb4e3b7750c0b