The United States Coast and Geodetic Survey put the machine into operation in 1910.

[2] Tides are the rise and fall of sea levels caused by the combined effects of gravitational forces exerted by the Moon, Sun, and rotation of the Earth.

In 1867 the United States Coast Survey started printing annual tide tables to support safe and effective maritime, coastal, and defense activities.

[2][3] Before long, these tables showed the times and heights of high and low tides to the nearest minute and tenth of a foot, respectively.

[3][4] The prediction of tides is very challenging as it depends on multiple factors–including the alignment of the Sun and Moon, the shape of the coastline, and near-shore bathymetry.

[3] To significantly reduce the work required to predict tides, in 1881 William Ferrel of the Coast and Geodetic Survey designed a tide-predicting machine.

[4] Rolin Harris and E. G. Fischer of the Coast and Geodetic Survey led the effort.

[6] The machine, also known as “Old Brass Brains”, used an intricate arrangement of gears, pulleys, slides, and other components.

The dials and scales made it much easier for an operator to precisely determine the height and time of high and low tides.

The paper graph, referred to as a tide curve, was very useful as a record of the computation that could be checked later to confirm the calculations were performed correctly.

[6] A hand crank turned by the operator provides the power for the machine’s mechanical calculations.

Battery-powered electrical circuits are used to mark the start of hours and days on the paper graph and to stop the machine when high and low tides were reached so the operator can note the height and time.

Also, the summation chains were moved across gears under tension for a year of work days before being installed in the machine to ensure they were sufficiently flexible and their length would remain constant.

Then the machine was disassembled, polished, plated, lacquered, and reassembled in time to provide predictions for the 1914 tide tables.

[5] Comparisons of the accuracy of the mechanical predictions of tides compared to hand calculations for two challenging locations demonstrated errors in heights of 0.72 inches (1.83 cm) or less.

Those factors are determined empirically by harmonic analysis of a time series of tides at the location,[6] and represent the influence of the moon, sun, depth of bay, offshore islands, etc.

[2] Around 1915, the machine was used to produce annual tide tables for 70 major ports worldwide.

During World War II the Coast and Geodetic Survey produced annual tide tables for major ports four years in advance in case Old Brass Brains broke down or was sabotaged.

Obtaining tide observations for those locations to support computation of the factors required for predictions was often a significant challenge.

[3] Around 1960 Old Brass Brains was modified to replace the hand crank with an electric motor and to add an automatic readout of heights and times.

2, 55 years after it entered service, and started performing its tide calculations with an electronic computer.

[2] The National Oceanic and Atmospheric Administration (NOAA) maintains Tide-Predicting Machine No.

This approach, called “harmonic analysis,” approximates tide heights by a summation of cosine terms, each of which has a different frequency.

This is the equation computed by most tide-predicting machines, including Old Brass Brains which handles 37 such terms.

[10] The longer sample minimizes the errors introduced by wind storms, freshets, and other non-regular influences.

As a result of this arrangement when the drive-wheel rotates uniformly, say clockwise, the shaft moves sinusoidally up and down.

An operator adjusted the location of each pin based on the empirically computed parameters for a port’s tides.

The Coast and Geodetic Survey designers also adopted from the earlier British machines the approach of summing terms by passing a chain over and under pulleys attached to the vertically oscillating yokes.

A similar arrangement of components on the other side, but with cranks 90 degrees out of phase, represents the derivative with respect to time of the tide height formula.

An electrical circuit detects this condition and stops the machine so the operator can record the date, time, and tide height.