Make Easyr Hydraulic Slide Rule, UK
Model None given. Made by the Easyr Slide Rule Co, Birmingham
1. This is a special rule produced for calculating velocities in sewers and pipes for given sizes and gradients.
2. Its binding gives the impression of being red leather.
3. The rule allowed the use of two different formulae; Kutter and Crimp & Bruges. Instructions in its use are given here.
4. The design has the registration  number 508,576. From 1884 design registration in the UK followed a consecutive numbering  system (unlike patents at that period). The first registered design in 1907 was 486,464 and in 1908 was 516,375. This dates the registration, and probably the rule, to 1907.
5. The pipe dimensions are those of a "standard" sewer. A newer shape was introduced before 1890. The use of the earlier cross-section helps to fix its date of manufacture toward the date of registration rather than later.
6. The address of the maker is given without a postcode. Postcodes were introduced in most big cities in the 19th century or early 20th, again suggesting an early date.

Rule closed
9904-hydraul01.jpg (13495 bytes)

Gilt embossed name
9904-hydraul02.jpg (16251 bytes)

Rule opened
9904-hydraul03.jpg (24526 bytes)

Circular pipes
9904-hydraul05.jpg (16727 bytes)

Egg-shaped sewers
9904-hydraul06.jpg (14985 bytes)

Pipe dimensions
9904-hydraul07.jpg (15938 bytes)

Detail -scales
9904-hydraul04.jpg (56793 bytes)

Alternative scale
9904-hydraul08.jpg (24753 bytes)

Manufacturing date Registered in 1907 and probably made at that time.
Length 16 cm
Material Cardboard. When closed it gives the appearance of a small Moroccan leather bound book with marbled edges to the pages.
Scales Special scales for sewerage pipes running completely or partially full.
Cursor None
Documentation None
Condition Very good.