Glossary

Spirit level

A hand tool with a bubble in a liquid tube that shows when something is perfectly flat (level) or upright (plumb). Used to set a level datum line.

A spirit level is a straight tool with a small tube of liquid and an air bubble in it. When the bubble sits dead centre between the two marks, whatever the level rests on is flat and level. Most levels have a second tube to check upright, called plumb.

On a gate job you use it to set a level line to measure from, to stand posts up straight, and to check the top of a gate is not running downhill. A 1200 mm box level is the common size; a small torpedo level fits in a pouch for quick checks.

For a long opening, pair a straight length of timber with a level, or step up to a laser level which throws a level line right across the site.

Related terms

Datum lineA line that is perfectly flat and level. You stretch it across an opening and measure from it, so every measurement starts from the same place.
String lineA thin line pulled tight between two points to mark a straight edge or a level line on site. The cheapest and most trusted setting-out tool.
SetoutMarking where the posts, gates, and panels will go on the real ground before any digging starts. The last chance to catch a measuring mistake.
PlumbVertical, true to gravity. A plumb post stands at exactly 90 degrees to a level horizontal datum. Out-of-plumb is the most common gate-install fault.
SquareAt exactly 90 degrees to a reference. A square gate frame has all four corners at right angles. Out-of-square frames don't sit right and bind on hardware.