# Lesson Notes By Weeks and Term - Senior Secondary 1

Diagonal and chordal scales

TERM – 2ND TERM

WEEK FIVE

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:

Subject: Technical Drawing

Topic: DIAGONAL AND CHORDAL SCALES

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

I.) Define a diagonal scale

II.) Differentiate between a diagonal scale and a chordal scale.

III.) Construct a diagonal scale and a chordal scale

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures,

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

 PRESENTATION TEACHER’S ACTIVITY STUDENT’S ACTIVITY STEP 1 INTRODUCTION The teacher Differentiate a diagonal scale from a chordal scale Students listens attentively to the teacher STEP 2 EXPLANATION Teacher guide students to construct diagonal scale and chordal scale. Students exhibit attentiveness and active engagement STEP 3 NOTE TAKING The teacher writes a summarized note on the board The students copy the note in their books

NOTE

DIAGONAL AND CHORDAL SCALES

Diagonal scale

A diagonal scale is a type of scale used in technical drawings, maps, and blueprints to represent distances accurately at different scales. Diagonal scale is used to read lengths with higher accuracy as it represents a unit into three different multiple in metres, centimeters and millimeters. It consists of a series of diagonal lines or bars, each representing a specific unit of measurement.

To construct a diagonal scale:

1. Determine the ratio of the scale (e.g., 1:100, 1:50, etc.).
2. Draw a horizontal line to represent the actual length or distance you want to measure.
3. Divide this line into equal parts according to the ratio (e.g., for a 1:100 scale, divide the line into 100 equal parts).
4. Draw diagonal lines from each division point to the corresponding point on a vertical line labeled with the actual lengths or distances.
5. Label the diagonal lines with the corresponding measurement units.
6. Ensure accuracy by double-checking your calculations and measurements.

Chordal scale

A chordal scale, also known as a string scale, is a type of scale used in engineering and technical drawings to represent distances accurately at different scales. It consists of a series of arcs or circles with their radii corresponding to different units of measurement.

To construct a chordal scale:

1. Determine the ratio of the scale (e.g., 1:100, 1:50, etc.).
2. Draw a horizontal line to represent the actual length or distance you want to measure.
3. Choose a suitable radius for your arcs based on the scale ratio and the length of the line.
4. Draw a series of arcs with centers on the horizontal line and radii corresponding to the units of measurement.
5. Label the arcs with the corresponding measurement units.
6. Ensure accuracy by double-checking your calculations and measurements.

EVALUATION: 1. Differentiate between diagonal scale and chordal scale

1. Construct a chordal scale.

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively