| Description | Date | Identifier | |
| Letter regarding the return of loaned apparatus to the Royal Aircraft Establishment, Farnborough. | 15th Dec 1931 | Box 165 \ 4 img134 | |
| Letter to North & Sons, Ltd. regarding a faulty Watford Magnetic Type Speedometer and requesting a replacement. | 30th Dec 1931 | Box 165 \ 4 img135 | |
| Letter from North & Sons, Ltd. acknowledging a request and confirming a modified speedometer will be sent. | 2nd Jan 1932 | Box 165 \ 4 img136 | |
| Request to despatch a Watford speedometer to Messrs. North & Sons for repair and adjustment. | 23th Jan 1932 | Box 165 \ 4 img137 | |
| Letter regarding the return of a Watford 100 m.p.h. speedometer for overhaul, repair, and adjustment. | 23th Jan 1932 | Box 165 \ 4 img138 | |
| The despatch of a faulty 100 M.P.H. Watford speedometer for an approval test. | 22th Feb 1932 | Box 165 \ 4 img139 | |
| Letter concerning the return of two inaccurate 100 M.P.H. speedometers due to poor performance during testing. | 22th Feb 1932 | Box 165 \ 4 img140 | |
| Request to despatch a replacement 100 m.p.h. magnetic type Watford Speedometer. | 23th Feb 1932 | Box 165 \ 4 img141 | |
| The return of a sample Watford 100 M.P.H. magnetic speedometer to the stores. | 3rd Mar 1932 | Box 165 \ 4 img142 | |
| Inquiry to Dobbie-McInnes & Clyde Ltd. regarding the suitability of their 'Farnboro' Electric Indicator. | 8th Mar 1932 | Box 165 \ 4 img143 | |
| The 'Maximum Pressure Indicator' apparatus for measuring pressure in engine cylinders. | 9th Mar 1932 | Box 165 \ 4 img144 | |
| Description of how a pressure gauge records maximum cylinder pressure and its A.I.D. approval for Type Tests. | 9th Mar 1932 | Box 165 \ 4 img145 | |
| Photograph of an engine mounted on a test rig, with a focus on the instrumentation. | 18th Feb 1932 | Box 165 \ 4 img146 | |
| Blueprint diagram of an Electrical Indicator Valve. | 18th Feb 1932 | Box 165 \ 4 img147 | |
| Wiring diagram showing the electrical connections for a pressure gauge system. | 9th Mar 1932 | Box 165 \ 4 img148 | |
| Quotation for a 'Farnboro' Electric Indicator and associated parts from Dobbie McInnes & Clyde Ltd. | 14th Mar 1932 | Box 165 \ 4 img149 | |
| Proposal for a new lightweight aero engine revolution counter using a small alternator. | 6th Mar 1932 | Box 165 \ 4 img150 | |
| Continued memo on testing a scheme with a Ferranti rectifier instrument for potential use in aero engines. | 6th Mar 1932 | Box 165 \ 4 img151 | |
| Inquiry to Vickers Aviation Ltd. regarding the type of electrical revolution indicator used on their multi-engine machines. | 22th Mar 1932 | Box 165 \ 4 img152 | |
| Letter from Vickers (Aviation) Limited regarding the electrical revolution indicators used on their multi-engined machines. | 23th Mar 1932 | Box 165 \ 4 img153 | |
| Request for particulars of electrical aero revolution indicating instruments from two separate companies. | 24th Mar 1932 | Box 165 \ 4 img154 | |
| Letter to Vickers (Aviation) Ltd. regarding Electrical R.P.M. Indicators. | 24th Mar 1932 | Box 165 \ 4 img155 | |
| Letter inquiring about a 'strobophonometer' for measuring engine noise and its potential use in detonation tests. | 29th Jun 1932 | Box 165 \ 4 img156 | |
| Letter from the Anglo-Persian Oil Company discussing engine noise measurement techniques using a Strobophonometer. | 1st Jul 1932 | Box 165 \ 4 img157 | |
| Continuation of a letter discussing engine knock testing equipment and procedures. | 1st Jul 1932 | Box 165 \ 4 img158 | |
| Gear ratios and performance compromises for a Bensport speedometer drive. | 5th Jul 1932 | Box 165 \ 4 img159 | |
| Speedometer calibration calculations for a Bentley 3 1/2 Litre chassis. | 7th Jun 1933 | Box 165 \ 4 img160 | |
| Testing and ordering of a Lucas bicycle lighting generator for use as an aero engine revolution indicator. | 6th Jul 1932 | Box 165 \ 4 img161 | |
| Requesting the return of a sample Watford 100 m.p.h. speedometer to Messrs Norths. | 13th Aug 1932 | Box 165 \ 4 img162 | |
| Letter to Mr. Stansfield of the Anglo Persian Oil Company arranging a meeting to discuss the Strobophonometer. | 26th Aug 1932 | Box 165 \ 4 img163 | |
| Letter to Mr. Everett of Anglo-Persian Oil Co. Ltd regarding suggestions for the Strobophonometer. | 30th Aug 1932 | Box 165 \ 4 img164 | |
| Sending notes regarding an electrical aero engine revolution counter and noting commercial interest from other companies. | 31th Aug 1932 | Box 165 \ 4 img165 | |
| Letter to the Anglo-Persian Oil Company Ltd. concerning the capabilities of a Strobophonometer instrument. | 2nd Sep 1932 | Box 165 \ 4 img166 | |
| Notes on the use of the Strobophonometer for detecting detonation. | 1st Sep 1932 | Box 165 \ 4 img167 | |
| Procedure for examining noises in a 12-cylinder engine and determining permissible detonation using a Strobophonometer. | 1st Sep 1932 | Box 165 \ 4 img168 | |
| Experiments and conclusions regarding the measurement of engine detonation and the potential use of a strobophonometer. | 8th Sep 1932 | Box 165 \ 4 img169 | |
| Leaflet for speed-indicating equipment from the B.T.H. Company. | 8th Nov 1932 | Box 165 \ 4 img170 | |
| Letter from British Jaeger Instruments Ltd. regarding a request for information on flexible lengths for two experimental instruments. | 8th Dec 1932 | Box 165 \ 4 img171 | |
| Cover letter accompanying a descriptive leaflet for Jaeger revolution counters. | 31th Dec 1932 | Box 165 \ 4 img172 | |
| French product information sheet for Jaeger recording tachometers. | 31th Dec 1932 | Box 165 \ 4 img173 | |
| French-language document from Jaeger describing the mechanism and operation of a recording tachometer. | 31th Dec 1932 | Box 165 \ 4 img174 | |
| Instruction page for operating a Jaeger tachymeter-recorder. | 1st Nov 1932 | Box 165 \ 4 img175 | |
| French-language table detailing graduations and revolution times for Jaeger precision instruments. | 1st Nov 1932 | Box 165 \ 4 img176 | |
| Letter to Westinghouse Brake & Saxby Signal Co. Ltd. providing patent application numbers for an Electrical Revolution Indicator. | 11th Mar 1933 | Box 165 \ 4 img177 | |
| Request to despatch a dismantled speedometer to Messrs S. Smith & Sons. | 21th Mar 1933 | Box 165 \ 4 img178 | |
| Letter from Westinghouse regarding competing patent applications for an electrical revolution indicator. | 30th Mar 1933 | Box 165 \ 4 img179 | |
| Letter to Westinghouse Brake & Saxby Signal Co. Ltd. regarding a German patent number. | 31th Mar 1933 | Box 165 \ 4 img180 | |
| Calibration and accuracy issues of Bensport speedometers. | 5th Mar 1933 | Box 165 \ 4 img181 | |
| Request to the Experimental Department to calibrate two temperature warning devices. | 29th May 1933 | Box 165 \ 4 img182 | |
| Letter to S. Smith & Sons Ltd. regarding errors found in revolution indicators for Bentley chassis. | 30th May 1933 | Box 165 \ 4 img183 | |
| Letter to Messrs. North & Sons Ltd. regarding test results of a sample speedometer and rev counter for a Bentley chassis. | 31th May 1933 | Box 165 \ 4 img184 | |
| Letter from North & Sons, Ltd. arranging a meeting to discuss a speedometer and rev counter for a Bentley Chassis. | 1st Jun 1933 | Box 165 \ 4 img185 | |
| Letter from S. Smith & Sons acknowledging an inquiry about A.T. Revolution Indicators for Bentley Chassis. | 1st Jun 1933 | Box 165 \ 4 img186 | |
| The calibration test results for a temperature warning device. | 7th Jun 1933 | Box 165 \ 4 img187 | |
| Reporting a speedometer reading discrepancy due to its steel mounting plate and requesting new plates made of Phosphor Bronze for trial. | 21th Jun 1933 | Box 165 \ 4 img188 | |
| The testing and modification of a Watford experimental speedometer for a Bensport chassis. | 27th Jun 1933 | Box 165 \ 4 img189 | |
| Letter from AC-Sphinx offering their newly manufactured magnetic speedometers for testing. | 29th Jun 1933 | Box 165 \ 4 img190 | |
| Bentley speedometer calibrations and the unresolved issue of tyre selection. | 30th Jun 1933 | Box 165 \ 4 img191 | |
| Bentley speedometer calibrations regarding tyre variations and a rev counter red segment recommendation. | 1st Jul 1933 | Box 165 \ 4 img192 | |
| Letter to Messrs. North & Sons Ltd. regarding the incorrect calibration of a Watford Speedometer. | 1st Jul 1933 | Box 165 \ 4 img193 | |
| Requesting the return of a Watford Speedometer to North & Sons for correct calibration. | 1st Jul 1933 | Box 165 \ 4 img194 | |
| Letter to the AC-Spinx Sparking Plug Co. Ltd. regarding a request for a speedometer sample for inspection and testing. | 3rd Jul 1933 | Box 165 \ 4 img195 | |
| Letter from North & Sons, Ltd. regarding the recalibration and return of a speedometer. | 4th Jul 1933 | Box 165 \ 4 img196 | |
| Querying if a previous instruction to hold an invoice from S. Smith & Sons for an Indicator Meter and Generator still applies. | 6th Jul 1933 | Box 165 \ 4 img197 | |
| The ongoing testing of an Electrical Revolution Indicator and holding the invoice in abeyance. | 7th Jul 1933 | Box 165 \ 4 img198 | |
| Letter from the AC-Sphinx Sparking Plug Co. Ltd. confirming a sample of a speedometer is being prepared. | 10th Jul 1933 | Box 165 \ 4 img199 | |
| Recalibrating speedometers on the 20/25 HP chassis due to customer complaints about them reading too fast. | 11th Jul 1933 | Box 165 \ 4 img200 | |
| Speedometer calculations and adjustments for the 20/25 chassis. | 11th Jul 1933 | Box 165 \ 4 img201 | |
| Requesting Bentley revolution indicators be ordered to read 2% fast to account for accuracy and temperature errors. | 12th Jul 1933 | Box 165 \ 4 img202 | |
| Letter regarding the specifications and approval of speedometers from S. Smith & Sons Ltd. | 12th Jul 1933 | Box 165 \ 4 img203 | |
| Instructions for checking the revolution indicator and speedometer on every Bentley chassis. | 13th Jul 1933 | Box 165 \ 4 img204 | |
| New electrical revolution indicator or tachometer, with attachments. | 15th Jul 1933 | Box 165 \ 4 img205 | |
| Letter proposing a new electrical speedometer for potential use in motor-cars and aero engines. | 14th Jul 1933 | Box 165 \ 4 img206 | |
| Solutions for adapting Bentley tail lights for Continental use. | 15th Jul 1933 | Box 165 \ 4 img207 | |
| Required alterations for an experimental Watford Revolution Indicator. | 17th Jul 1933 | Box 165 \ 4 img208 | |
| Request to order a Klaxon electric motor for a Bensport revolution counter test rig. | 19th Jul 1933 | Box 165 \ 4 img209 | |
| Instruction to fit a Watford speedometer and rev indicator from chassis IB.IV to the Green Bentley 2.B.IV chassis. | 19th Jul 1933 | Box 165 \ 4 img210 | |
| Proposed electrical revolution indicator, its potential applications and limitations. | 20th Jul 1933 | Box 165 \ 4 img211 | |
| Outlining testing parameters and acceptable limits for the Bentley Revolution Indicator. | 20th Jul 1933 | Box 165 \ 4 img212 | |
| Clarifying the maximum instrument temperature and RPM limits for the Bentley Rev Counter. | 21th Jul 1933 | Box 165 \ 4 img213 | |
| Internal order for a synchronous electric motor for a Bentley revolution counter test rig. | 21th Jul 1933 | Box 165 \ 4 img214 | |
| New electrical revolution indicator or tachometer. | 21th Jul 1933 | Box 165 \ 4 img215 | |
| Letter regarding drawings for a tachometer that operates on a frequency measurement principle rather than voltage. | 17th Jul 1933 | Box 165 \ 4 img216 | |
| The testing and rejection of faulty Bentley speedometers submitted for approval. | 22th Jul 1933 | Box 165 \ 4 img217 | |
| Letter to W.G. Bird regarding an Electrical Revolution Indicator, enclosing pamphlets and drawings. | 24th Jul 1933 | Box 165 \ 4 img218 | |
| Speedometer calibration calculations for a Bentley 3 1/2 Litre chassis based on different tyre and axle configurations. | 27th Jul 1934 | Box 165 \ 4 img219 | |
| Recommendation to purchase two types of electrical revolution indicators for testing on aero engine test beds. | 27th Jul 1934 | Box 165 \ 4 img220 | |
| Letter to Messrs North & Sons Ltd. regarding a faulty Watford Revolution Indicator for a Bentley chassis. | 10th Aug 1933 | Box 165 \ 4 img221 | |
| Letter from North & Sons, Ltd. regarding the testing and calibration of a Watford Revolution Indicator. | 14th Aug 1933 | Box 165 \ 4 img222 | |
| Letter from North & Sons Ltd regarding the testing and accuracy of an intermittently operated counter. | 14th Aug 1933 | Box 165 \ 4 img223 | |
| Return of a faulty Watford revolution indicator clock from a Bentley chassis for repair. | 5th Sep 1933 | Box 165 \ 4 img224 | |
| Confirming arrangements to mount a new Klaxon Synchronous motor for a speed counter calibration test rig. | 12th Sep 1933 | Box 165 \ 4 img225 | |
| Agreement with Messrs. Smith to exhibit a 20/25 HP instrument patch but not a Bentley one. | 9th Oct 1933 | Box 165 \ 4 img226 | |
| Letter concerning the exhibition of a Rolls-Royce and a Bentley Instrument Patch at Olympia. | 9th Oct 1933 | Box 165 \ 4 img227 | |
| Visit to A.T.Co.Ltd to dispute an extra charge for a modification to Bentley rev counters. | 10th Oct 1933 | Box 165 \ 4 img228 | |
| Acceptance of costs for alterations to Bentley Rev. Counters. | 14th Oct 1933 | Box 165 \ 4 img229 | |
| Inquiry regarding the minimum distance between instruments to prevent magnetic interference, specifically the speedometer, ammeter, and petrol gauge. | 29th Dec 1933 | Box 165 \ 4 img230 | |
| Speedometer revolutions per mile for a 40/50 HP car, requesting a correction to a drawing. | 2nd Jan 1934 | Box 165 \ 4 img231 | |
| Quotation from Dobbie McInnes & Clyde Ltd for a 'Farnboro' Electric Indicator' and associated Disc Valve Units. | 3rd Jan 1934 | Box 165 \ 4 img232 | |
| Letter to Dobbie, McInnes & Clyde Ltd. regarding a trial of a new 'A' Disc Valve Unit. | 8th Jan 1934 | Box 165 \ 4 img233 | |
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