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Fearns, Fearns Mear & Co, and M H Mear made a wide range of specialist circular calculators and M H Mear continues to make them at Ramsden Mills, Britannia Road, Milnsbridge, Huddersfield, UK; their range can be viewed on their website. The calculators in my collection are from Fearns, Fearns Mear and M H Mear.
Fearns Calculators, Oakfield Drive, Whickham, Newcastle-upon-Tyne, England, Inches - Millimetres Conversion Calculator. Single sided with rotating cursor. Table of fractions to decimals and instructions on reverse. Complete with vinyl slip case. Five inches diameter.
Fearns Calculators, Oakfield Drive, Whickham, Newcastle-upon-Tyne, England, Weight Calculator for Plates & Sheets. Single sided with rotating inner disc and rotating transparent half disc/cursor. Complete with vinyl wallet. Combined imperial and metric. 7.6 inches diameter.
Weight Calculator for Castings & Forgings. Fearns, Mear & Co, 43 St Helens Road, Almondbury, Huddersfield. Single sided with rotating inner disc and rotating transparent cursor. Imperial only. Heavy duty cloth covered card slip case. 7.6 inches diameter.
The Fearns-Mear Standard Machining Time Calculator for Lathework Model No 2. Fearns, Mear & Co, 43 St Helens Road, Almondbury, Huddersfield. A double sided imperial calculator. The front side has one rotating disc; the reverse has three rotating elements. Instructions are printed on both sides of the calculator for different operations. 7.5 inches diameter. Heavy duty cloth covered card slip case with paper table of horsepower requirements on it

A detailed history of the firms, written by Colin Barnes, appears in Issues 2 and 3 of the Slide Rule Gazette, published by the UKSRC, from which the following has been extracted.
Norman Mear started designing and selling circular calculators in 1947 initially from ivorine, which was subject to distortion, and then from cast acrylic Perspex.  The first calculator was a Gas Flow Calculator, believed to have been made for him by Abbott Brown & Co of Beaminster. The business was initially part time and did not become full time for Norman Mear until 1957 when he gave up working for W C Holmes. The first calculators were sold under the name of  N Mear, 22 Stanley Road, Lindley, Huddersfield. In 1956 Mear moved to St Helens Road, Huddersfield and it may have been about this time that he met Stanley Fearns. By c1957 Fearns, Mear & Co were trading from St Helens Gate, Huddersfield (the Mear’s family home) and the business was rapidly growing with an increasing number of calculator designs. The partnership continued until 1962 when it was dissolved and the two firms of Fearns and M H Mear started trading separately, each with their own specialised (different) range of calculators. Fearns factory was the “Atlas Works”, Dunstan, near Newcastle, Whickham Drive being the office address. The firm of Fearns appears to have ceased trading in the early 1980s.  M H Mear had works in Rook Street, Huddersfield from 1962 and continued to be a family firm after the death of Norman Mear in 1980 until its sale in 1994 to Mr J M V Mosley. In 1964 M H Mear moved to 56 Nettleton Road, Dalton, Huddersfield and were still there, under Mr Mosley’s ownership until at least 2001, later moving to Britannia Mills, Ramsden Road.
Fearns “Farmers Weekly Metric Converter and Slide Rule” ©1970. Around the periphery are a large number of gauge points used for imperial to metric conversion. Inside is a “D” scale used for both conversion and multiplication with the “C” scale printed onto the transparent second disc. There is also a cursor. The instructions are printed on the reverse along with an index to the conversion factors. It is 5½ in diameter and has a green PVC wallet.
The Fearns Belt Conveyor Calculator. This double sided circular calculator is 7.5 inches diameter and has one revolving disc on the upper side and two revolving parts on the under side. It is complete with PVC wallet and three instruction leaflets which are contained in a transparent pocket on the back of the PVC wallet. It also catered for elevators. As all the scales are imperial it probably dates from the 1960s.
Fearns Ratefixer’s Calculator for Estimating Speeds, Feeds & Cutting Times. This double sided plastic calculator, 7.5 inches diameter, is metric one side and imperial the other. It is actually a basic machining time calculator intended to assist with piecework rate calculations for drilling, milling and turning. Each side has a rotating inner disc and transparent sector. It has a PVC wallet.
Consett Iron Co Ltd Weight Calculator for Steelwork. Double sided plastic calculator, 7.5 inches diameter, with one rotatable disc each side. Imperial only, made by Fearns Mear & Co, 43 St Helens Rd, Huddersfield, c1960. The first side is for rolled steel sections and the second for  cylinders, plates, tubes and bars. The instructions for use are given on each side. It has a heavy duty cloth covered card slip case.
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AUDCO  Pipe Flow Calculator for Liquids and Gases made by  Fearns Mear & Co, 43 St Helens Rd, Huddersfield, for the Audel Engineering Co Ltd, Newport, Shropshire. It was used to calculate the flow rate in gallons/hour(liquids) or cu.ft/hour (gases) given the pipe diameter, specific gravity, viscosity and pressure drop. It was only suitable for turbulent flow and the reverse of the calculator was for the calculation of Reynolds Number to check that the flow was turbulent (i.e. Re > 2000). It is complete with instruction leaflet and vinyl sleeve. This was one of the earliest calculators made by Fearns Mear and is made of Ivorine - it exhibits the distortion that this material was prone to. Price new was 15 shillings, c1958.
Hall Bros (West Bromwich) Ltd Weight Calculator for Steelwork. Double sided plastic calculator, 7 3/4 inches diameter, with one rotatable disc each side. The metric version, made by M H Mear & Co. The first side caters for a wider range of rolled steel sections than the one above. It has a PVC wallet
M H Mear Warm Air Heating Calculator Model No. 3. A double sided 7 ¾ inch diameter calculator with one rotating disc each side. Detailed instructions are printed on the calculator itself. It has PVC wallet.
M H Mear Comprehensive Conversion Calculator, 5.7” diameter, made for INOMA Ltd. It has conversions for a wide range of mechanical engineering parameters, such as length, volume, pressure, weight. It has a blue vinyl wallet.
Knight Strip Metals Ltd weight & length calculator, 7.6” diameter, made by Fearns Calculators, Oakfield Drive, Whickham , Newcastle-upon-Tyne. Imperial one side and metric the other. It has a brown vinyl wallet. For coils of strip metal.
Fearns Calculators A61 Re-Order Point Calculator. Single sided 7.5” diameter. It has a brown vinyl wallet and a sales leaflet for it and other calculators.
Fearns Calculators no. A62 Economic Order Point Calculator. 7.5” diameter with Purchase Discount Evaluator on the reverse. It has a brown vinyl wallet.
M H Mear Psychrometric calculator for calculating relative humidity from wet & dry bulb thermometer readings, etc. It has an instruction booklet and a vinyl wallet.
Fearns Mear timber calculator supplied by M H Mear & Co, 43 St Helens Rd, Huddersfield. This double sided calculator has a green cloth covered card case. The instructions are in the centre of each side of the calculator that can be used to calculate quantities and prices. Ca.1962. 7.6 inches diameter.
M H Mear & Co, 43 St Helens Rd, Huddersfield warm air heating calculator. This is essentially the same as the one shown earlier but is imperial instead of metric. This double sided calculator has a green cloth covered card case. The instructions are in the centre of each side of the calculator that can be used to calculate duct sizes, pressure loss, etc. Ca.1963. 7.6 inches diameter.
A H Cole (Tools) Ltd, Rubery, Rednal, Birmingham “Cole-Draulic” valve sizing calculator for hydraulic pressing operations. Copyright M H Mear & Co, Huddersfield, 1975 who were the makers of this calculator. The instructions for use are given in the centre. It is 5 3/4 inches diameter. Valve flow is calculated from the press stroke, piston area and travel, and number of strokes per minute. A valve is then selected having this capacity. Given the pressure in the system it can also be used to find the total holding force.
Fearns Shaft Size & Horsepower calculator made for Allspeeds Ltd, makers of variable speed gears. It has a flexible PVC wallet that may not be original.
Fearns tank capacity calculator made for Kenneth Forbes (Plastics) Ltd. It has a flexible PVC wallet. It can be used to calculate the capacity of both rectangular and cylindrical tanks including the latter when partially full. Capacity can be read in cubic metres, litres, Imperial and US gallons, and cubic yards. Dimensions are input in feet and inches. 5.5 inches diameter.
Fearns Bonus Calculator new in September 1968. A single sided calculator with one rotating disc and transparent cursor. It is 5” diameter. It is complete with the original card postal box, invoice and advice notes, and a leaflet advertising other Fearns calculators. For calaulating the percentage bonus payable based on time taken to complete a batch of items. There is a conversion table for decimal hours and minutes.
Fearns Calculators, Oakfield Drive, Whickham, Newcastle-u-Tyne Machining Time Calculator for Drilling, Reaming & Tapping. It is a 7.5” diameter, double sded calculator with two rotating segments on one side and a rotating disc on the other. It is complete with vinyl case, table of feeds, and instruction leaflet. Imperial so likely to be 1960s.
Fearns Calculators, Oakfield Drive, Whickham, Newcastle-u-Tyne Machining Time Calculator for Milling. It is a 7.5” diameter, double sded calculator with three rotating segments on one side and a rotating disc on the other. It is complete with vinyl case, table of horsepower required at spindle per inch width of cut, and instruction leaflet. Imperial (and still called Fearns Mear) so likely to be 1960s.