Definition
A unit of electrical power equal to one one-thousandth of a watt (0.001 W). Used to express very small amounts of power, such as the signal strength of weather balloon transmitters and other low-power radio equipment.
Plain English
A tiny unit of power. One thousand milliwatts make up one watt.
Context Anchor
Seen in upper-air observation discussions when describing small electronic instruments carried by weather balloons or other weather-sensing equipment.
Derivation
From the Latin 'mille' meaning 'thousand', combined with 'watt' (the standard unit of power, named after Scottish engineer James Watt). The prefix 'milli-' always signals one-thousandth of the base unit.
Why Pilots Care
Weather balloon radiosondes transmit on very low power -- often just a few hundred milliwatts -- yet their data feeds the upper-air charts and forecasts pilots rely on for flight planning.
Analogy
If 1 watt were divided into 1,000 equal pieces, each piece would be 1 milliwatt.
Grounding Statement
A small weather instrument can send a radio signal using only milliwatts of power because the receiving equipment is built to detect weak signals.
Intuition Check
A milliwatt is small, not large. 'Milli-' means one-thousandth, not one million. A 250-milliwatt transmitter puts out a quarter of a single watt.
Example Sentence 1
The radiosonde carried aloft by the weather balloon transmits its data on roughly 400 milliwatts of power.
Example Sentence 2
Many battery-powered aviation sensors are designed to operate in the milliwatt range to conserve energy.