Meshtastic-Android/docs/developer/measurement.md

title, nav_order, last_updated, aliases

title	nav_order	last_updated	aliases
Measurement & Formatting	9	2026-05-13	measurement metric-formatter number-formatter

Measurement & Formatting

How the Meshtastic Android/KMP app formats numbers, units, and locale-sensitive values.

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Overview

All measurement data transmitted by Meshtastic radios uses metric units (meters, °C, hPa, m/s, etc.). The app converts and formats these values for display using two core utilities:

Utility	Location	Purpose
MetricFormatter	core/common/.../util/MetricFormatter.kt	Converts and formats physical measurements (temperature, pressure, speed, etc.)
NumberFormatter	core/common/.../util/NumberFormatter.kt	Low-level fixed-point number formatting with locale-independent dot separator

Both live in org.meshtastic.core.common.util and are available to all KMP targets (Android, Desktop, iOS).

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MetricFormatter API

MetricFormatter is a Kotlin object with pure functions for each measurement type:

object MetricFormatter {
    fun temperature(celsius: Float, isFahrenheit: Boolean): String
    fun voltage(volts: Float, decimalPlaces: Int = 2): String
    fun current(milliAmps: Float, decimalPlaces: Int = 1): String
    fun percent(value: Float, decimalPlaces: Int = 1): String
    fun humidity(value: Float): String
    fun pressure(hPa: Float, decimalPlaces: Int = 1): String
    fun snr(value: Float, decimalPlaces: Int = 1): String
    fun rssi(value: Int): String
    fun windSpeed(metersPerSecond: Float, decimalPlaces: Int = 1): String
    fun rainfall(millimeters: Float, decimalPlaces: Int = 1): String
}

Usage

// Temperature — Fahrenheit conversion is handled automatically
MetricFormatter.temperature(22.5f, isFahrenheit = true)  // "72.5°F"
MetricFormatter.temperature(22.5f, isFahrenheit = false)  // "22.5°C"

// Signal metrics
MetricFormatter.snr(-5.2f)    // "-5.2 dB"
MetricFormatter.rssi(-97)     // "-97 dBm"

// Environment
MetricFormatter.pressure(1013.25f)  // "1013.3 hPa"
MetricFormatter.humidity(65.0f)     // "65%"
MetricFormatter.windSpeed(3.7f)     // "3.7 m/s"
MetricFormatter.rainfall(12.3f)     // "12.3 mm"

// Power
MetricFormatter.voltage(3.95f)      // "3.95 V"
MetricFormatter.current(125.0f)     // "125.0 mA"

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NumberFormatter

NumberFormatter provides locale-independent decimal formatting using pure arithmetic (no String.format or DecimalFormat):

object NumberFormatter {
    fun format(value: Double, decimalPlaces: Int): String
    fun format(value: Float, decimalPlaces: Int): String
}

Why locale-independent? Meshtastic is a mesh networking app where consistency matters — sensor readings shared between nodes should look the same everywhere. NumberFormatter always uses . as the decimal separator.

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Temperature Conversion

Temperature is the only measurement that performs a unit conversion. The isFahrenheit flag is typically sourced from the user's device locale or preferences:

°F = °C × 1.8 + 32

All other measurements display in their native metric units. The user-facing units-and-locale.md page explains what end users see.

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Adding a New Measurement Type

To add a new measurement formatter:

1. Add a function to MetricFormatter in core/common/src/commonMain/kotlin/org/meshtastic/core/common/util/MetricFormatter.kt:

   fun radiation(microSieverts: Float, decimalPlaces: Int = 2): String =
       "${NumberFormatter.format(microSieverts, decimalPlaces)} μSv/h"
   

2. Add tests in core/common/src/commonTest/:

   @Test
   fun radiationFormatting() {
       assertEquals("0.15 μSv/h", MetricFormatter.radiation(0.15f))
       assertEquals("1.23 μSv/h", MetricFormatter.radiation(1.234f))
   }
   

3. Use in UI — call from any commonMain composable or ViewModel:

   Text(text = MetricFormatter.radiation(node.radiationLevel))
   

4. Run verification:

   ./gradlew :core:common:allTests
   

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DateFormatter

Date and time formatting uses the DateFormatter interface with platform-specific implementations:

Function	Output Example
formatRelativeTime()	"5 min ago"
formatDateTime()	"May 13, 2026 2:30 PM"
formatShortDate()	"May 13"
formatTime()	"2:30 PM"
formatTimeWithSeconds()	"2:30:45 PM"
formatDate()	"2026-05-13"

Unlike MetricFormatter, DateFormatter is an interface with platform expect/actual implementations because date formatting inherently depends on platform locale APIs.

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Design Decisions

Decision	Rationale
Locale-independent decimal separator (.)	Mesh data shared between nodes must be consistent
Pure arithmetic formatting (no DecimalFormat)	Works identically on JVM, Native, and JS targets
Temperature is the only converted unit	All other metric units are universally understood in their native form
object singleton pattern	Stateless utility — no instance management needed

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Related

• User-facing docs: docs/user/units-and-locale.md explains what end users see
• Source code: core/common/src/commonMain/kotlin/org/meshtastic/core/common/util/MetricFormatter.kt
• Tests: core/common/src/commonTest/kotlin/org/meshtastic/core/common/util/MetricFormatterTest.kt