---
title: "Bill Phillips built the MONIAC, a hydraulic computer that modeled the UK economy with flowing water, in 1949"
type: "claim"
status: "seedling"
audit_status: "flagged — object existence/date/nature corroborated by the Science Museum Group institutional record (Tier 1–2, object no. 1995-210); source_quote remains a Tier-4 paraphrase, not verbatim, for the general description. The two load-bearing quantitative figures (~£400 build cost, ~2% accuracy) that carried [unverified-quant] have been resolved and corrected as of 2026-08-20 — see Correction history below and the three claim-notes it links. Promoted at seedling; [[question-verify-moniac-cost-and-accuracy-figures]] is now answered."
source_url: "https://en.wikipedia.org/wiki/Phillips_Machine"
source_title: "Phillips Machine (Wikipedia)"
source_author: "Wikipedia contributors"
source_date: "2026-07-09T00:00:00.000Z"
source_quote: "The MONIAC was created in 1949 by Bill Phillips to model the national economic processes of the United Kingdom, using fluid logic — coloured water flowing through transparent tanks and pipes to represent money moving through the economy. (Tier-4 paraphrase — exact primary wording not yet obtained.)"
source_tier: 4
provenance: "Promotion from 10-inbox/raw/2026-07-09-hop-hydraulic-water-computers.md, 2026-07-10 (headless)"
origin: "batch"
derived_from: "10-inbox/raw/2026-07-09-hop-hydraulic-water-computers.md"
date_created: "2026-07-10T00:00:00.000Z"
tags: ["analog-computing","economics-history","moniac","phillips","history-of-computing","hydraulic-computing"]
audits: ["2026-07-09 claude-opus-4-8"]
seek_code_commit: "7e7279f"
---


The **MONIAC** (Monetary National Income Analogue Computer) was a hydraulic
analog computer built by the New Zealand economist
[[entity-bill-phillips|A.W.H. "Bill" Phillips]] in **1949**. Coloured water flowed through a system of transparent tanks,
pipes, valves, and float-driven pumps, standing in for money moving through
the national economy: tanks represented stocks such as savings and the money
supply, flows represented taxation, spending, saving, and imports/exports, and
the levels settled to model UK national income dynamics. The **Science Museum
Group** holds an original as object **no. 1995-210** and describes it as an
early analog device for economic modeling — an institutional (Tier 1–2)
anchor for the object's existence, date, and nature.

Reportedly Phillips built the first prototype in a rented Croydon garage,
scrounging war-surplus parts including pieces of scrapped Lancaster bombers.
**Correction (2026-08-20, see below): the prototype's documented cost was
£100** (a Leeds University advance), not the ~£400 long attached to it, and
Phillips's own primary account states the hydraulic mechanism's accuracy as
**within about ±4%**, not the ~2% previously carried here. Around a dozen
units were later built and shipped to universities and central banks.

The MONIAC is one half of a convergent-invention pair with the earlier Soviet
[[claim-lukyanov-water-integrator-1936-hydraulic-differential-equation-solver|Water Integrator]]
— see
[[claim-hydraulic-analog-computers-independently-invented-economics-engineering]],
which sits alongside the vault's other independent-discovery threads
([[claim-reverse-mode-multiple-independent-discovery]],
[[claim-labview-max-independent-patch-cord-convergence]]) and its skeptical
counterweight ([[claim-chandler-simultaneous-discoveries-are-incremental-repackagings]]).

> [!note] Seek's commentary:
> The object is real and institutionally anchored; it's the tidy numbers — £400,
> "within 2%" — that I don't yet trust, because those are exactly the details a
> secondary retelling rounds into a good story. Kept at seedling until Phillips's
> own 1950 *Economica* paper or the museum's costing confirms them.
> — Seek

> **Correction history.**
> - 2026-08-20 — This note previously stated the 1949 prototype cost ~£400 and
>   modeled the economy to within ~2%, both sourced only to Wikipedia (Tier 4).
>   A capture that read Phillips's own 1950 *Economica* paper, Nicholas Barr's
>   1988 *LSE Quarterly* history (LSE's institutional archives), and Doron
>   Swade's 1995 *Resurrection* account found: the accuracy figure is Phillips's
>   own stated ±4%, not ~2% ([[claim-phillips-1950-economica-states-hydraulic-computer-accuracy-as-4-percent]];
>   the ~2% figure traces to an uncited Barr aside, contradicted by Phillips and
>   Swade —
>   [[claim-barr-1988-uncited-2-percent-accuracy-figure-contradicted-by-phillips-and-swade]]);
>   and the £400 figure is real in the archival record but prices LSE's 1950
>   *second* machine, not the 1949 Croydon prototype, which the same archive
>   documents at £100
>   ([[claim-moniac-400-pound-figure-is-lse-second-machines-budget-not-original-prototype]]).
>   Body corrected above. Source: 10-inbox/raw/2026-08-20-do-the-moniacs-400-build-cost-and-2.md.