Metric Precision Worksheet
Physical Science & Math Grade 7 • Lab Measurement Skills
Metric Ruler Precision Practice
Name:
Date:
Period:
Conversion Rule: 1 cm = 10 mm • Count mm ticks as tenths of a centimeter (e.g., 4.7 cm = 47 mm).
Precision: Nearest 0.1 cm (1 mm)
1
Direct Alignment: Measure Each Object from Zero
Object A: Steel Machine Pin
Length: cm Length: mm
0 1 2 3 4 5 6 7 8 9 10 cm
Object B: Copper Test Wire
Length: cm Length: mm
0 1 2 3 4 5 6 7 8 9 10 cm
2
Offset Measurement: Calculate Length When Starting Past Zero
Object C: Mineral Crystal Core
Start: cm End: cm Length: cm ( mm)
0 1 2 3 4 5 6 7 8 9 10 cm
Object D: Preserved Lab Specimen
Start: cm End: cm Length: cm ( mm)
0 1 2 3 4 5 6 7 8 9 10 cm
3
Pointer Precision: Read Specific Marks Along the Scale
P Q R S 0 1 2 3 4 5 6 7 8 9 10 11 12
Pointer P
cm:
mm:
Pointer Q
cm:
mm:
Pointer R
cm:
mm:
Pointer S
cm:
mm:
4
Lab Analysis & Measurement Thinking
4A. Plant Growth Observation
An Elodea shoot measured 4.8 cm on Day 1 and grew to 8.3 cm by Day 5.
Total Growth in cm:
Total Growth in mm:
4B. Measurement Precision
A student records a slide width as 2.548 cm using a standard metric ruler marked in millimeters.
Why is this precision invalid for this tool?
Metric Measurement • Grade 7 Lab Skills Page 1 of 2 Self-Assessment: □ Units labeled □ Subtraction checked
Teacher Reference Solutions & Scoring Rubric
Metric Ruler Practice — Answer Key
Total: 20 pts
Formative Guide
Part 1: Direct 4 pts (1 pt cm, 1 pt mm)
Part 2: Offset 6 pts (Start, End, Length)
Part 3: Pointers 8 pts (1 pt cm, 1 pt mm each)
Part 4: Lab Thinking 2 pts (1 pt math, 1 pt concept)
Part 1: Direct Alignment Solutions
Allow ±0.1 cm (±1 mm) tolerance
Object A (Steel Pin): 5.7 cm = 57 mm
Starts at 0.0 cm and aligns with 7th mm mark past 5 cm.
Object B (Copper Wire): 8.4 cm = 84 mm
Starts at 0.0 cm and ends 1 mm before the 8.5 cm mark.
Part 2: Offset Measurement Solutions
\(\text{Length} = \text{End} - \text{Start}\)
Object C (Mineral Crystal):
- • Start: 2.3 cm (23 mm) • End: 8.8 cm (88 mm)
- • Length: \(8.8 - 2.3 = \mathbf{6.5\text{ cm}}\) (\(\mathbf{65\text{ mm}}\))
Error note: Check for ignoring start offset (writing 8.8 cm).
Object D (Preserved Specimen):
- • Start: 3.6 cm (36 mm) • End: 9.1 cm (91 mm)
- • Length: \(9.1 - 3.6 = \mathbf{5.5\text{ cm}}\) (\(\mathbf{55\text{ mm}}\))
Error note: Watch for counting ticks backwards.
Part 3: Pointer Precision Solutions
1 pt cm + 1 pt mm each
Pointer P
1.8 cm
18 mm
2 mm before 2.0
Pointer Q
4.5 cm
45 mm
Exact mid-tick
Pointer R
7.2 cm
72 mm
2 mm past 7.0
Pointer S
10.9 cm
109 mm
1 mm before 11.0
Part 4: Lab Analysis Solutions & Grading Criteria
4A. Plant Growth Calculation
• Difference: \(8.3\text{ cm} - 4.8\text{ cm} = \mathbf{3.5\text{ cm}}\)
• Millimeters: \(3.5 \times 10 = \mathbf{35\text{ mm}}\)
Award full credit if both values and units are present.
4B. Measurement Precision
Model Answer: The ruler's smallest increment is 1 mm (0.1 cm). A value like 2.548 cm claims certainty to thousandths of a cm (0.01 mm), which exceeds the resolution of this instrument.
Criteria: Identifies ruler increment limit (mm/0.1 cm).
Key Remediations & Lab Bench Habits
1. Off-by-one tick count: Remind students to count line intervals (spaces) rather than boundary lines.
2. Decimal placement: Emphasize that 5.7 cm = 57 mm (never 5.7 mm or 570 mm).
3. Parallax error: Keep eyes directly perpendicular above the specimen when aligning ends with ticks.
Metric Measurement • Grade 7 Lab Skills Answer Key Page 2 of 2 Standards: CCSS.MATH.CONTENT.7.EE.B.3 • NGSS SEP-3
