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I will be adding more slide rules to these pages as my collecting progresses as there are more than a hundred known rules by Blundell Rules Ltd and Blundell Harling, as well as hundreds of slide charts and other specials.
Blundell Rules Ltd Humidity Slide Rule Mk 6, Ref No MET 22000, MO 3247/68. A specialist plastic slide rule with reversible cursor for scales on reverse. For calculating relative humidity from wet and dry bulb thermometer readings. Complete with card case.
Blundell Rules Ltd, Met Office Humidity Slide Rule Mk IV. Farenheit version, the Celsius Mk 6 is shown below. A duplex plastic rule with reversible cursor. The scales are: used to calculate vapour pressure,  relative humidity and dew point from psychrometer readings. It has a green, cloth covered card case.
Paper Facts & Figures Paper Calculating Rule ©1965. Open frame plastic construction slide rule with instructions and further scales on reverse. For calculating the weight of various quantities of paper in both standard and non-standard sizes. Complete with blue cloth covered card case. Although not marked as such was almost certainly made by Blundell Harling who also made a metric version, see below. The blank is that used for the Academy 300 series.
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Wavin Pipe Friction Computer and Metrication Converter made by Blundell Harling no. P3259 for Wavin Pipes United Kingdom Ltd, ©1969, designed by A D Calthorpe, C.Eng, MICE, AMIWE. Ii is based on an Academy Duplex blank and has a card stiffened vinyl wallet case and a laminated instruction slip. One side is imperial and the other metric but both sides perform the same function and the double sided cursor can be used to convert any parameter from imperial to metric or vice versa., Scales are labelled A to G with outside them inch or cm scales (above) and gallons or litres scales (below). The computing scales are: A -  gauge marks for different classes of  BS PVC pipe and nominal diameter, B - pipe internal diameter, C and D - flow rate in different units, E - pipe length, F -  friction loss (head), G - friction loss {pressure).
Fisher Control Valve Sizing Rule Mark VII made by Blundell Harling (P2734) for GEC-Elliott Control Valves Ltd, Rochester, England. ©1967. This duplex plastic rule has 17 specialist scales for gases, steam and liquids from which the size parameters Cv, Cg or Cs can be determined given pressure drop, inlet pressure and flow rate, specific gravity (liquid) or inlet density (gas/vapour), temperature and degree of superheat (steam). The rule has a fabric backed PVC slip case. This is an imperial rule. A metric mark VIE by IWA is illustrated in the “Other German” page. Several versions of the Fisher rule were made including one by Pickett for the American Fisher company.
The metric version of the Paper Facts & Figures Paper Calculating Slide Rule ©1969, P3188. This is a duplex rule with fifteen specialist scales covering both paper and board. It has a quality vinyl wallet and instruction booklet.
Fisher Control Valve Sizing Rule Mk V, Blundell Harling P2734A ©1967. This is also an imperial rule, made of green plastic. It has a leather slip case. It is shorter than the one above but the scales appear to be the same.
Blundell Rules Ltd P2297 Torpedo Spreading Slide Rule Pattn. No. 0552-160221 dating from about 1964, made for the Royal Navy. It has two slides and was used to calculate the firing interval for a salvo of torpedoes given the target range and speed, its length and the desired spread, as well as angle to bow on firing. It has a varnished wood case.
This bearing rate slide rule was almost certainly made by Blundells even though it is not signed. It has a wood case which is also entitled Bearing Rate Slide Rule Mark 1 Model 0 but has the Pattern no 0552-160219 on it. It was made for the Royal Navy.
Fisher Control Valve Sizing Rule Mk IV, P2355 ©1966, This is a nine inch scale length duplex slide rule. It has a PVC slip case.
Rule Slide 10” MK3/1 hade by Blundell Harling. It is a variant of the Omega 401 Rietz slide rule made for the British army. Unlike the standard Omega 401 but typical of British army slide rules it has two cursors. The scales are the standard Rietz ones, K,A{B,C1,C}D,L//{S,ST,T}.
Weight calculator for steel sections made for Cashmores by Blundell Harling number P4108 (ca. 1972)
Armstrong Calculator made by Blundell Rules Ltd, Weymouth, no. P1553, ca. 1962. It has a light blue cloth covered card case with Armstrong Calculator on it. The scales are for calculating the area of flooring, the number of tiles and the price. Made for the Armstrong Cork Co Ltd, Bush House, London WC2.
ICI Slide Rule for Calculation of Diameter of Orifice Plates with Corner Taps. Plastic, made by BRL no. P1454 ca. 1961. It has a blue cloth covered card case. Serial no? 316.
Blundell Harling P4603 Mk III Orifice Slide Rule ca.1975. Made for ISA Controls Ltd/W J Clark. This duplex rule has imperial scales one side and metric ones the other. It has a blue/clear PVC slip case.
Blakeborough Valve Sizing  Slide Rule and valve chart made by Blundell Rules Ltd in Weymouth. The chart is dated October 1959. The upper face was used for liquid flow to calculate the flow coefficient Cv on which basis the correct size of valve could be selected from the chart. The lower face was for gas and steam flow.
Blundell Rules Ltd, Weymouth, P1442 Friction Loss Calculator made for Shell-Mex and BP Ltd. Fabricated from plastic, there is no cursor and the slide is reversible. The scales on the body front are: pipe length ft actual, pipe length ft equiv, friction loss ins W G (inches water gauge). The slide has instructions on one side together with scales of flow rate in BTU/HR for three values of temperature difference and in gallons/hr for 3/4” copper pipe, and similar scales for 1/2” copper pipe on the reverse. The back of the rule has tables on it for emission  for radiators, and 1/2” and 3/4” copper pipe. Ca.1962.
Blundell Omega Slide Rule Artillery 10” Mils Mk 2. A closed frame slide rule made of plastic with two plastic cursors (replacements). Scales are A{B,C}D//{S,ST,T}. The trig scales are in mils (6400 mils = 360 degrees). There is a metres at 1/50,000 rule on the upper edge extension and there are instructions and formulae on the back. NATO stock number 1290-99-960-0933. Green cloth covered card case
Blundell Omega Slide Rule Artillery 10” Mk 3. A closed frame slide rule made of plastic with a plastic cursor (probably should be two). Scales are A{B,C}D//{S,ST,T}. The trig scales are in degrees. There is a metres at 1/50,000 rule on the upper edge extension and there are instructions and formulae on the back. NATO stock number V6/1290-99-960-0934. Green cloth covered card case
Blundell Harling Pilot Balloon Slide Rule Mk5. Developed by the British Meteorological Office to enable the user to compute readings taken from observations taken from Pilot Balloons, Met Ref No 29550. The 24 3/4 inch LOA rule is plain on the back apart from the notice illustrated. Serial No 4022/68 made in 1968.
Paper Facts & Figures Rapid Paper Costing Slide Rule. Blundell Harling P3808. It has a paper instruction sheet. ©1971. See also two other Paper Facts & Figures slide rules earlier on this page.
BRL “Lidderdale” P2145 slide rule for calculating areas and volumes. It has instructions and a blue/clear PVC wallet.
Nelson-Jones slide rule for electronics engineers made by Blundell Harling (P4277) for Key Electronics. Scales are: dB, A{B,C1,C)D,LL3,LL3//XL{L&C,Frequency)XC. It has a black PVC slip case and instructions.
Blundell Rules Ltd P2327 10” plastic slide rule made for the Metal Box Co to calculate percentage overlap. It has a blue plastic case that may not be original and is missing its cursor.
Blundell  P4310 10” plastic slide rule made for the Metal Box Co to calculate actual overlap. It has a blue plastic case. The instructions are on the reverse of the slide.
Heath & Co, New Eltham “Hezzanith” Carmody Navigation Slide Rule made by BRL. It has a black leatherette covered wood case. Scales are in\LL2,A{B,C1,C}D,LL3//{S,ST,T}. In addition there are a cm ruler and a table on the reverse.
BRL P2808 ultrasonic slide rule made for Sandt (JWF registered design). It has a PVC slip case and instructions but is missing its cursor. It is intended for calculating the parameters associated with the ultrasonic testing of welds and flaw detection.