1. Conversions

2. 34m = _________ km

3. 46 inches = __________ Feet

4. 3.4 MJ = ________ J

5. 2.9x107nl = _______ GL

6. Significant Digits

7. Measurements Every measurement is wrong! Examples: To a certain degree
Your Birthday
Height

8. Every measurement has a degree of uncertainty
The uncertainty is based on:
The measuring device
The skill of the measurer

9. Ways to indicate How Accurate a Number Is
Tolerance Intervals
Percent Error
Significant Digits

10. Tolerance Intervals
Tolerance is the greatest range of variation that can be allowed
25  0.5 would be between to 25.49
25  0.05 would be between to
25  would be between to

11. Tolerance Intervals
Used on blueprints and in machining to indicate accuracy

13. Activity: Tolerance a Part
Design a square piece with a square hole through it’s centre.
Key Dimensions:
How must the length of the piece be toleranced
How big must the square hole through the piece be to accommodate the square peg
Criteria:
The square piece must sit inside a container that was toleranced 20m  lm on each side
The square peg is dimensioned 2m 0.1m

14. Percent Error
Indicates a percentage that the value may be out by

15. Sample Problem
You buy an 8 foot 2x4. You measure the board to be 94.5 inches long. What is the percentage error for the length of the board?
12 inches = 1 foot

16. Significant Digits The accuracy is determined by the right most digit
25 would be between to 25.49
25.0 would be between to
25.00 would be between to

17. Significant Digits: Uses the number of digits in the number to express the uncertainty of the number
1 x 101 is less accurate than 12
12 is less accurate than 12.0
12.0 is less accurate than 12.00

18. Rules for Significant Digits
All non-zero digits are significant
All zeros contained between non-zero digits are significant
i.e. 207 – 3sd
All trailing zeros to the right of a decimal are significant
i.e – 4sd

19. When are zeroes not significant?
All leading zeros to the left of the first non-zero digit are not significant
i.e – 2 sd

20. Exact numbers have infinite significant digits
How many cars do I have? 1

21. Examples
a.) 125.9
b.) 230
c.)
d.) 500.3

22. Examples:
a.) s.d.
b.) s.d.
c.) s.d.
d.) s.d.

23. How to Improve Accuracy
Improve the measuring instrument
The smaller the unit on the measuring device, the more precise the measurement
Know how to measure
Always look straight down on the measuring device
Repeat
Measure several times to get a good average value
“Measure twice, cut once”
Measure under controlled conditions
Objects can shrink or expand based on measuring conditions

24. Why wouldn’t you make everything very, very accurate?
Cost
Waste of time
Not needed
The more accurate a measurement must be, the more it costs to do so

25. Bibliography
Britton. "Geometric Dimensioning and Tolerancing." Lecture. nicaldesign101/GDandT.pdf. 1 Feb. 2013