# Plumb Bob (Sahaal) in Construction

> A plumb bob, or sahaal, is a weight on a string that gives a true vertical line. See how masons check formwork with it and how SuperWise records the check.

Canonical: https://superwise.site/glossary/plumb-bob/
Last updated: 2026-11-01

A pointed metal weight hung from a string to give a true vertical line when checking walls and formwork.

## What is Plumb Bob (Sahaal)?

A plumb bob, called a sahaal on Indian sites, is an ancient surveying tool made of a dense, pointed metal weight hung from a string. Gravity pulls the string into a true vertical line, called a plumb line. Masons and carpenters use it to check that walls and [formwork](https://superwise.site/glossary/formwork/) stand straight up and down.

## Practical example

A carpenter is erecting formwork for a 3-metre tall wooden column. Before tightening the final braces, they hang a plumb bob down the side of the wood. The string is 2 inches from the wood at the top but only 1 inch at the bottom, so the formwork leans and must be adjusted before the concrete is poured.

## In SuperWise

In SuperWise a checklist can hold a Yes/No field for the plumb check, a Photo field for the plumb line against the shuttering and a Signature field for the [site engineer](https://superwise.site/glossary/site-engineer/). Attached to the formwork task with enforcement on, the task cannot be completed until the filled form is approved.

[Quality and safety checklists](https://superwise.site/features/construction-quality-safety/)

## Related terms

- [Site Engineer](https://superwise.site/glossary/site-engineer/)
- [Formwork (Shuttering)](https://superwise.site/glossary/formwork/)

## Related
- [Site Engineer](https://superwise.site/glossary/site-engineer/)
- [Formwork (Shuttering)](https://superwise.site/glossary/formwork/)
- [Quality and safety checklists](https://superwise.site/features/construction-quality-safety/)