Old instruments

Sector Instrument

Direct answer

Sector Instrument is a two-legged mathematical instrument carrying paired scales whose spacing solves proportional problems.

Sector Instrument is a hinged proportional calculator used in historical astronomy, timekeeping, or navigation.

Historical Almanacs & InstrumentsThe Great Almanac DictionaryUpdated 2026-09-26

Get my personal reading

$0 today, then $12/month after 7 days. Cancel anytime.

At a glance

Found in: Historical Almanacs & Instruments
Related: Equinoctial Ring Dial, Gunter's Quadrant, Dioptra, Alidade

A brass sextant, a mariner’s astrolabe and a pair of dividers — Instrument plate · visual guide **Sector Instrument**
Sector Instrument is a hinged proportional calculator used in historical astronomy, timekeeping, or navigation.
An engraved functional orientation; the page explains the real instrument, method, or publication.

From the reference page to your own chart

What does your own chart say about you?

Choose love, work or purpose. Your reading is written from your chart. Your reading uses your own birth details.

Get my personal reading $0 today, then $12/month after 7 days. Cancel anytime.

Walk through Alex’s whole example first

The Road of AgesSee the turning points of your whole life, from your birth date See your road's shape

Prefer to explore first?

Member tools The 2026 book Lectures

The daily letter, free

One short letter at 7 each morning: the day’s theme read for your own chart.

The Road of AgesThe turning points of your whole life, from your own chart Walk my road

Free, by email

Your daily Almanac letter

One short letter at 7 each morning: the day’s theme read for your own chart, and one thing to do with it.

The story behind Sector Instrument

Sectors served gunners, surveyors, navigators, artists, and astronomers from the late Renaissance onward.

A one-minute story

The Book of the Sky

How people learned to read the sky, from Babylon to the day you were born.

Why Sector Instrument matters

Sector Instrument matters because opening the legs turns geometric similarity into a flexible analogue calculator.

Where readings of Sector Instrument go wrong

The sector does not calculate automatically; using the wrong scale or opening changes the proportion.

Sources and editorial method

Research references used for this entry include:

Royal Museums Greenwich: Astronomical and Navigational Instruments - Museum reference collection for historical observing, calculating, timekeeping, and navigation instruments.

Source: The Great Almanac Dictionary
Category: Historical Almanacs & Instruments
Last updated: 2026-09-26

Explore Sector Instrument

A definition tells you what it is; your own birth chart tells you what it means for you. The Oracle casts your real chart and answers for your love, your work, and your year ahead, in conversation. It opens with the 7-day Seeker trial.

Speak with the Oracle

Equinoctial Ring DialEquinoctial Ring Dial is a portable universal sundial used in historical astronomy, timekeeping, or navigation. Gunter's QuadrantGunter's Quadrant is a portable astronomical quadrant used in historical astronomy, timekeeping, or navigation. DioptraDioptra is an ancient sighting instrument used in historical astronomy, timekeeping, or navigation. AlidadeAlidade is a sighting rule used in historical astronomy, timekeeping, or navigation. AlmanacAn Almanac is a date-organized reference that gathers practical yearly information. Nautical AlmanacThe Nautical Almanac supplies yearly celestial data for navigational sight reduction.

More in Historical Almanacs & Instruments

From the reference page to your own chart

Every word here
is in your own chart.

A personal reading about love, work or purpose, written from your chart
A practical next step to consider
It opens with 7 days free, with the AI Oracle and daily guidance