Description and Notes:
The Fowler's Calculators Ltd. was a Manchester based company established in 1898. According to a historical record provided by the Collections Department of Museum of Science & Industry (MSI), Manchester, their "Magnum" Long Scale calculator was introduced in 1927.
With an impressive outer diameter of 4¾ inches, the circumference of this calculator is about 15 inches. Save a small rusty spot at the lower left edge of the backplate, this item is well perserved over the years and still in excellent working order. As shown in the picture above, it comes with the original leather wallet and instruction booklet. The address of the Fowler's Ltd. printed on the instruction booklet is Hampson Street, Manchester, and, hence, this device is dated to c1940, as according to the source of the MSI mentioned above, the company was moved to the address in 1938. In the instructions the merits of the calculator is described as follows:
Fowler's "Magnum" Calculator, like the well-known waistcoat pocket instrument consists of a series of concentric circular scales, logarithmically divided and mounted on a dial capable of rotation by a thumb nut outside the containing case. The scales are equipped with a fixed radial datum line, and a radial cursor line rotated by a second thumb nut. The rotating scales cursor line, and operating mechanism are enclosed in a metal containing case, fitted with a glass face so that the scales are always kept clean, and the instrument is preserved from external injury in a handsome wallet which fits easily into a side pocket.
The large size of the "Magnum" enables all the scales to be mounted on one dial, and so of being synchronised and read concurrently. It also permits of the use of larger figures and easier reading, an advantage to persons of weak eyesight. Another important feature is that the scales are longer and admit of finer graduation and more accurate reading. This is specially noticeable in the "Long-Scale" which gives a length of 50 ins. as compared with 10 ins in the ordinary slide-rule and permits of calculations being made to four, and sometimes five, significant figures. The motions of the scales and cursor can be made with great ease and nicety and there is none of the objectionable sticking or slackness often so troublesome with the straight, slide rule, nor is there any of the "end switching" often necessary with that instrument when working with the full length scale and which induces many users to work habitually with the half length. In circular calculators the scales are continuous and there is no half length.
To sum up the merits of Fowler's "Long-Scale" Instruments, they are more portable, comprehensive and accurate; cleaner and easier to operate, and may be used equally well in any climate.
Save it only has one dial which contains four major scales (log, sqr roots, sine, tan) in circular form, the basic operation of this calculator is the same as that of the Russian KL-1. As shown in the picture above, the top turning knob is for rotating the dial, and the side one is for the pointer.