In 1949, Keynsian economist Bill Phillips (father of the Phillips curve) built the financephalograph, also known as the MONIAC, which stands for Monetary National Income Analogue Computer. Using water to represent money, the massive hydraulic model of a national economy was, for a time, the most complex, and wettest, economics computer in the world.

The MONIAC on display in the Reserve Bank Museum is one of 14 built. It was originally owned by the London School of Economics and calibrated to represent the British economy. A second MONIAC, linked to the first, represented the rest of the world.

The MONIAC is one of the most popular exhibits in the Reserve Bank Museum and Education Centre and remains an impressive demonstration of engineering and economic expertise. MONIAC Moniac demonstrations are held on the first Wednesday of the month between 12:15 and 12:45 p.m.

In 1990, the MONIAC was brought to New Zealand by the New Zealand Institute of Economic Research and refurbished, including re-calibration to the New Zealand economy.

In 1990 it was lent to the Reserve Bank Museum and Education Centre and further refurbishment work was done. Leakage is always a risk, and the display cabinet in which it is installed has been specially built with drainage and a drip tray.

The MONIAC is capable of making complex calculations that could not be performed by any other computer at the time. The calculations are based on Keynesian and classical economic principles, with various tanks representing households, business, government, exporting and importing sectors of the economy.

Water pumped around the system can be measured as income, spending, and GDP. The system is programmable, and experiments with fiscal policy, monetary policy, and exchange rates can be carried out.

Besides the working MONIAC at the Reserve Bank of New Zealand, MONIAC machines can also be seen at Istanbul University, Cambridge University, and London's Science Museum.