kWh Cost / Energy Bill Estimator

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Electrical & Electronics Engineering — Circuits, Power Systems, Electronics Lab

Tranche

tranche-5

Evidence ID

t5-213

Ledger rows

1

No ledger note is attached.

Review findings

The honest-label statement is appropriate for v1: the estimator uses a user-entered rate and is not connected to live utility billing. Before release, define the exact meaning of days, month, and year, explicitly document the W-to-kW conversion, and validate nonnegative finite numeric inputs.

Formula and scope findings

• The standard energy formula is correct only when P is expressed in kilowatts, but the declared input is power in watts; the required conversion P(kW)=power(W)/1000 is not stated in the formula.
• The formulas do not explicitly define total energy or cost for the supplied days input: energy_for_days=(power(W)/1000)×hours_per_day×days and cost_for_days=energy_for_days×rate are needed.
• The claimed monthly and yearly outputs are ambiguous because the specification does not define whether a month means 30 days, the actual calendar month, or an average month, and whether a year means 365 or 366 days.

Unit assumptions

• power is entered in watts (W) and converted to kilowatts by dividing by 1000.
• hours_per_day is measured in hours and must be nonnegative.
• days is a nonnegative day count; test vectors use 30 days for a nominal month and 365 days for a nominal year.
• utility_rate is in USD per kWh and is assumed nonnegative.
• Monthly results below use exactly 30 days; yearly results use exactly 365 days.
• Energy is reported in kWh and monetary outputs are reported in USD.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

The extreme finite-looking input values overflow ordinary JavaScript arithmetic and produce Infinity for energy and cost. The estimator needs range validation or explicit overflow handling. A second hazard is that the specification does not define a branch or physical limit at 24 hours/day, nor a calendar convention for month/year totals.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "power_W": 100,
    "hours_per_day": 5,
    "days": 30,
    "utility_rate_USD_per_kWh": 0.2
  },
  "expected_outputs": {
    "energy_per_day_kWh": 0.5,
    "energy_for_days_kWh": 15,
    "energy_per_30_day_month_kWh": 15,
    "energy_per_365_day_year_kWh": 182.5,
    "cost_per_day_USD": 0.1,
    "cost_for_days_USD": 3,
    "cost_per_30_day_month_USD": 3,
    "cost_per_365_day_year_USD": 36.5
  },
  "working": "100 W ÷ 1000 = 0.1 kW. Daily energy = 0.1 kW × 5 h = 0.5 kWh. Energy for 30 days = 0.5 × 30 = 15 kWh. Energy for 365 days = 0.5 × 365 = 182.5 kWh. Daily cost = 0.5 kWh × $0.20/kWh = $0.10. Cost for 30 days = 15 × $0.20 = $3.00. Cost for 365 days = 182.5 × $0.20 = $36.50."
}

Related workflows

No source-defined multi-instrument workflow membership is recorded.

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche5/tranche5-results.json
• BOUNDARY_HAZARD_CATALOG.json