Measurements and steel rules

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1. Topic Measurements and Steel Rules

2. For more help contact me Muhammad Umair Bukhari [email protected] www.bzuiam.webs.com 03136050151

3. History of Measurement Units of measurement were literally at our finger tips- hands, arms, feet, legs Common units of measurement is derived from Europeans recorded history These familiar units of measure are results of long evolutionary system

4. Standards of inches, feet, and yards are summarily divided by “common fractions” (1/2,1/4,1/8,1/16 etc, or decimal fractions(1 in, 0.1 in, 0.01in etc) used now-a-days in US. Rest of the world use “SI metric system” or “International system”

5. Basic unit conversions 1 m=100 cm 1 cm=10 mm 1 m= 39.37 inch 1 inch=2.54 cm 1 inch=25.4 mm

6. Steel rules Steel rules are simple instruments of linear assessment Usage: Fractional inches, usually to 1/64 th of an inch A decimal scale with a typical determination of 0.01 mm and half mm

7. Types of steel rule Rigid rules Flexible rules Narrow rule Hook rule Narrow hook rule Rule set Tapered end rule

8. Types of measurements Direct : Direct comparison with an established standard Indirect : Indirect measuring system identifies the difference between the object being measured and a known dimension. This type of measurements use comparators- those “transfer” instruments that contact and assess the work piece and then compared with an external scale which determines the amount of the expressed difference. Which is the actual dimension of the object. E.g. Calipers

9. Reference point to measure point Any linear measurement can be broken down into two points 1.References point 2.Measured point we set the instrument at reference point and move the instrument –or read along it-until we find the measure point

10. Errors in scale reading Look squarely at the face of a clock and read the time Then walk several feet to one side and honestly read the time The clock will read several mins slower or faster, depending on angle you view it from, normally done by all. It is called Parallax error.

11. Errors in scale reading Parallax error

12. Errors in scale reading If you move your head, nose, and eyes over a several inches from reference point to the measure point, you may find your hand, holding the rule, has unconsciously traveled with the body motion and moved the rule across the work, thus make an error in the measurement

13. Precautions in measurements Do not use dull and worn out instruments Do not cramp its style, be relax, loosen your grip Set the reference point in position and read the measured point Hold the rule lightly but firmly