Source: https://guthlabs.ai/docs/instruments/electricity-cost-of-appliance-calculator/

instrument / verified-clean

# Electricity Cost of Appliance Calculator

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

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Inspectable records

[01**Overview**Purpose and lifecycle](<https://guthlabs.ai/docs/instruments/electricity-cost-of-appliance-calculator/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/electricity-cost-of-appliance-calculator/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/electricity-cost-of-appliance-calculator/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/electricity-cost-of-appliance-calculator/qualification/>)

## Ledger state

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

**Area**: Everyday & Life

**Tranche**: tranche-4

**Evidence ID**: t4-258

**Ledger rows**: 1

No ledger note is attached.

## Review findings

The core energy and cost formulas are standard and correct under the stated units. Review is required to define the exact monthly and annual day-count conventions and to explicitly include hours_per_day × days in the total-energy formula. The honest-label warning about efficiency, duty cycle, and manually entered rates is appropriate; preset values should also identify their source and reference date.

### Formula and scope findings

- kWh = watts × hours / 1000 is correct when hours means total operating hours, but the declared input is hours/day plus days; the aggregation formula must explicitly be total_kWh = watts × hours_per_day × days / 1000.

- The mapping of days to monthly and annual outputs is unspecified: a month could mean 28–31 calendar days or a fixed 30-day period, and an annual result could mean 365 or 366 days.

- Daily cost is implied but not explicitly stated as daily_kWh × rate_per_kwh; the output definitions should specify whether monthly and annual values are derived from daily usage or from separately entered total hours.

### Unit assumptions

- Wattage is in watts (W), hours/day is decimal operating hours per day, and days is a count of days in the reporting period.

- Dividing by 1000 converts watt-hours to kilowatt-hours.

- Electricity rate is in dollars per kilowatt-hour ($/kWh), so cost is in dollars.

- For the test vectors, a monthly period means exactly 30 days and an annual period means exactly 365 days.

- Inputs represent actual energized operating time; standby consumption, variable power draw, and duty cycle are not modeled unless separately incorporated into the wattage or hours.

## Boundary hardening

**BREAK_CLAIMED** · SELF_FLAGGED

An extreme but numerically representable wattage causes JavaScript arithmetic overflow: 1e308 × 24 becomes Infinity, and all derived outputs become Infinity. The instrument should validate finite, reasonable inputs and reject or clearly report overflow.

## 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": {
    "appliance_wattage_w": 1500,
    "hours_per_day": 2,
    "electricity_rate_usd_per_kwh": 0.18,
    "days": 30,
    "period": "monthly"
  },
  "expected_outputs": {
    "daily_kwh": 3,
    "daily_cost_usd": 0.54,
    "period_kwh": 90,
    "period_cost_usd": 16.2
  },
  "working": "Daily energy = 1500 W × 2 h/day ÷ 1000 = 3000 Wh/day ÷ 1000 = 3 kWh/day. Daily cost = 3 kWh/day × $0.18/kWh = $0.54/day. Period energy = 3 kWh/day × 30 days = 90 kWh. Period cost = 90 kWh × $0.18/kWh = $16.20."
}
````

## Related workflows

[Off-Grid Solar Designerload audit](<https://guthlabs.ai/docs/instrument-workflows/solar-offgrid/>)

## 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-tranche4/tranche4-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`