Where to Aim: Floor Spots, Distance and Angle

Aim at the same clean spot, from the same distance and the same angle, every time. A gun is best used to compare readings with each other, and that only works when you hold the method steady.

The distance-to-spot ratio

A gun doesn't read a point. It reads a circle, and the circle gets bigger the farther away you stand. The distance-to-spot ratio, written D:S, links the two. If the D:S ratio is 12:1, the diameter of the measurement area is one-twelfth of the distance to the object¹.

Here's what that means in plain terms. Suppose your gun lists a ratio of 12:1 on its label. Standing 12 inches away, you read a circle about 1 inch wide. Standing 36 inches away, you read a circle about 3 inches wide. The same example appears in the source: a 12:1 device senses a 1-inch circle at a distance of one foot¹. Your gun's own ratio may differ, so look in its manual.

The target should be bigger than the spot. The ideal target area should be at least twice the size of the spot at that distance¹. On a floor, that means a clean patch of stone with room around your aiming point, not a narrow strip.

Not too close, not too far

A gun should not be placed too close to a hot target, because the closeness could cause heat to build up in its housing and damage the sensor¹. Standing far away has its own cost. The source ties error at long range to reflectivity and to the inclusion of other heat sources within the sensor's field of view¹. In an oven, those other sources could be hot walls or the flame.

The oven mouth is a hot place to hold your hand and the tool. Follow your oven's manual and the gun's manual for safe distances and for protective gloves. Never reach into a lit oven in a way the maker doesn't allow.

The red dot is only a guide

The visible dot plays no part in the measurement¹. It marks the middle. The circle read by the sensor is larger than the dot. So when the dot sits near a sooty patch, part of that patch can still be in the reading.

Choosing floor spots

Many wood-fired ovens have a round floor under a dome². Heat may not be even across it, and stone near the flame can differ from stone near the door. A few spots give a better picture than one.

1. Choose a spot in the centre of the floor, where the pizza will usually sit.
2. Choose a second spot to one side, at the same distance from the door.
3. Choose a third spot near the back, if you can see it safely.
4. Skip any patch with heavy soot, flour, ash or burnt food.
5. Skip shiny metal parts, such as a door or a thermometer housing.

The emissivity of a surface depends on its composition and structure³, so a patch of soot next to clean stone isn't comparable. See Emissivity: Why Shiny Surfaces and Soot Give Odd Readings.

The angle

Aim as straight at the floor as you can while keeping your hand clear of the opening. A shallow angle stretches the circle into an oval and can pull in more of the walls. Hold the same angle each session so your readings stay comparable. Your gun's manual may say more about the angle it expects.

Keep a record

A simple log helps more than any single reading:

• Date and fuel used.
• Spot names, such as centre, left, back.
• Distance and angle you used.
• The reading, and the time since lighting.

After a few sessions, you'll know what your floor looks like when it's ready, in the units your manual uses. For the dome side of the story, see Floor Temperature vs Dome Temperature.