# How to Measure Accurately with a Tape Measure

Accurate measurement is critical in FRC fabrication. Small errors can cause misaligned parts and poor assembly fit.

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</div>## Reference Edge (Most Important Rule)

Always measure from a consistent, known reference point. For FRC extrusion, this should be the **factory-cut end of the tube**.

This ensures every measurement starts from a true, flat surface.

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</div>## Using the Tape Measure

- Seat the hook firmly on the factory edge
- Keep the tape straight and tight
- Read at eye level to avoid parallax error
- Use the smallest increment you can reliably read

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</div>## Offset Measurement Method (High-Precision Technique)

For improved accuracy in tight tolerance work, you can use an offset method:

- Align the **1 inch mark** of the tape with the factory edge
- Read the measurement from that point
- **Subtract 1 inch from the final value**

This reduces small errors caused by hook movement or wear.

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</div>## Using a Speed Square for Marking

A speed square is used to create accurate 90° layout lines.

How to use it:

- Place the square’s fence against the factory edge
- Mark your measured point
- Draw a straight line across the extrusion using the square edge

This ensures:

- Square cuts
- Accurate drill lines
- Proper part alignment

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</div>## Common Mistakes

- Measuring from a damaged or non-factory edge
- Forgetting to subtract the 1 inch offset
- Letting the tape twist or sag
- Drawing marks without a square

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</div>## Key Idea

Accuracy comes from using a consistent reference edge and controlling measurement error through either direct reading or a properly applied offset method.