G1+ Gauge – Crack monitor with simplified reading

Technical specifications

G1+ or G1: the difference is in the reading

The G1+ gauge is installed and used exactly like the G1 gauge: it is a crack monitor fixed across the crack, with the same mounting methods and the same monitoring in the application. The difference lies in how the tenths of a millimetre are read.

The principle: the darkened row gives the tenths digit

1. The millimetres are read on the graduated scale: this is the graduation to the left of the triangular mark.

2. The tenth is read in the reading window, where 10 rows of lines are numbered from 0 to 9. Each time the sliding arm moves by 0.1 mm, a different row turns dark. The number of the darkened row is the tenths digit.

3. Two adjacent darkened rows mean that the mark is halfway between two tenths: read the intermediate value, for example 34.15 mm. This is what gives the G1+ its 0.05 mm resolution.

No parallax error when reading the tenths

On a vernier gauge such as the G1, the tenth is read by finding the vernier line that lines up with a line on the scale. The two scales are not in the same plane: if your eye is not directly in front of them, the apparent alignment can shift by one line, i.e. 0.1 mm. This is parallax error.

On the G1+, there is no line alignment to look for: you simply read the number of the darkened row. Reading the tenths is therefore not exposed to the parallax error caused by aligning lines, which also makes readings more consistent when several people take them in turn.

G1 gauge / G1+ gauge comparison

For a resolution of 0.01 mm with a digital display, and a removable gauge that does not stay on the surface between readings, see the E1 gauge – digital crackmeter.

How to read the G1+ gauge?

Reading takes two steps: the millimetres on the graduated scale, then the tenth in the reading window. The first reading only serves as a reference: it is the difference from the following readings that measures how the crack is changing.

Between the two readings, the crack has opened by 0.55 mm in 90 days (about 3 months).

The vernier at the top of the sliding arm can be used to confirm the reading to 0.1 mm, on the same principle as the G1 gauge (see how to read the vernier of the G1 gauge).

How to mount the G1+ gauge?

Two mounting methods are possible:

• By bonding: the gauge is fixed quickly and easily with the double-sided adhesive pads supplied. The surface must be smooth, dry and clean so that the adhesive is in contact over its entire area.
  If necessary, especially on rough surfaces (e.g. render), bonding can be reinforced with a fast-curing twin-syringe epoxy adhesive.
• By mechanical fixing: G1+ gauges are supplied with 2 pre-drilled Ø 4 mm holes, which make fixing with screws and wall plugs easy. A 4 mm hole can be drilled very easily in any surface.
  On difficult surfaces (crumbly, dusty, rough or damp), we recommend screw fixing to prevent any detachment. Packs of 50 screws and wall plugs are available, as well as a ready-to-use mechanical mounting kit including a 4 mm drill bit, a screwdriver and 40 wall plugs and screws.

Installation tips

To monitor changes in the crack as effectively as possible, the gauge is usually fixed where the crack is widest (often in the middle of the crack). The gauge can be fixed whatever the direction of the crack (vertical, horizontal, diagonal), across the crack, to measure changes in its width. The G1+ gauge is made of a material flexible enough to adapt to irregular, convex or concave surfaces.

Ideally, position the vernier triangle between 33 and 34, with the 2 speckled bands visible on the right and left. The aim is to centre the sliding arm. There is no need to place the mark on a precise graduation: the principle is to measure the difference between 2 readings. Whatever the value of the first reading, it becomes the zero point.

Note: the G1+ gauge does not measure movement along the crack (sliding). For this, use a G6 gauge, which measures movement on 2 axes in the plane.

How to measure a crack in a corner?

G1+ gauges manufactured from mid-2025 have a groove marking a fold line on the sliding arm. This groove makes it easy to fold the sliding arm for corner installation without any additional accessory.

Earlier versions of G1-family gauges were supplied with a folding bar for corner installation. An aluminium angle bar (sold separately) can also be used.

Examples of corner installation:

How to protect the G1+ gauge?

Gauges installed in public or high-traffic areas (schools, shops, streets…) may be damaged (torn off, graffiti…). To protect the gauge, we offer a UV-resistant protective cover, fixed with the wall plugs and screws supplied.

In high-traffic areas where the risk of damage is high, the removable E1 gauge with transparent plates can be used instead. After each reading, only the plates remain on the surface, which prevents any damage.

Download the Saugnac.app application to track your readings

The Saugnac web application, completely free and unlimited, is available on PC or smartphone at https://saugnac.app. It lets you:
– identify each G1+ gauge and its readings with its unique QR code
– save the readings taken in your account (manual entry for the G1+)
– retrieve the temperature and humidity via geolocation
– calculate readings corrected for thermal expansion based on temperature
– collaborate with several users on the same gauge
– manage alert thresholds
– sort gauges by place and locate them on a map
– download data in Excel format
– display graphs automatically
– share data with other people who do not have an account
– add readings offline

Find all the explanations on how the application works.

Download the Excel monitoring file

You can also download the Excel file for tracking G1+ readings .

This Excel file is very easy to use: simply duplicate a sheet for each site or project monitored, with each sheet tracking up to 10 gauges.

The file takes into account the expansion coefficient of the gauge body and the sliding arm, adjusting each reading according to the difference between the temperature at the time of the reading and that of the first reading. If you did not record the temperature, simply leave it blank: thermal expansion will then not be taken into account.

Note: the effect of thermal expansion on G1+ readings is small (approx. 9 µm per degree).

Frequently asked questions about the G1+ gauge

What is the difference between the G1 gauge and the G1+ gauge?

Installation, mounting and use are identical. The difference lies in how the tenths are read: the G1 is read with a vernier, by finding the line that lines up with the scale; the G1+ adds a reading window in which a numbered row turns dark at each tenth. Its resolution is 0.05 mm (compared with 0.1 mm) and its measuring range approx. 25 mm (compared with 20 mm). See the G1 / G1+ comparison.

Does the initial width of the crack matter?

No. The G1+ gauge does not measure the width of the crack, but how it changes. The first reading only serves as a reference, whatever its value: the differences between this reading and the following ones show whether the crack is opening, closing or stable. To find out the width of the crack on the day of installation, use a crack ruler or a triangular gauge. For a wide crack, the G1.3 gauge is designed for this purpose.

Simplified reading, “digital” reading: what does it mean?

Both terms refer to the same system. It has long been called “digital” reading because the tenth is read directly as a digit. The G1+ is nevertheless an entirely mechanical gauge, with no battery or electronics. For an electronic digital display to 0.01 mm, see the E1 gauge.

How do you read tenths of a millimetre on the G1+ gauge?

Find the darkened row in the reading window: its number, from 0 to 9, is the tenths digit. Add it to the number of millimetres read on the scale, to the left of the triangular mark. For example, 34 mm with row 7 darkened gives 34.70 mm. See how to read the G1+ gauge.

What do two darkened rows mean?

The mark is halfway between two tenths: take the intermediate value. With 34 mm on the scale and rows 1 and 2 darkened, the reading is 34.15 mm.

Why does the G1+ avoid parallax error?

With a vernier, you have to find two lines that line up even though they are not in the same plane: depending on the viewing angle, the apparent alignment can shift by one line, i.e. 0.1 mm. On the G1+, you read the number of a darkened row: there is no longer any line alignment to judge.

What is the vernier of the G1+ gauge used for?

It can be used to confirm the reading to 0.1 mm, on the same principle as the G1 gauge. Reading the tenths on the rows remains the main reading method.

Can the G1+ gauge be tracked with the Saugnac application?

Yes. The QR code on the gauge identifies it in the application, where readings are entered manually. The application plots graphs, manages alert thresholds, corrects for thermal expansion and lets you share data. Automatic reading from a photo is available for G1, G1.1 and G1.2 gauges, but not for the G1+.

G1+ gauge or E1 gauge: which one should you choose?

The G1+ stays fixed on the crack and is read with the naked eye, with a resolution of 0.05 mm. The E1 gauge is a removable digital crackmeter with a resolution of 0.01 mm, positioned on plates fixed on either side of the crack: only the plates remain on the surface between readings. In both cases, readings are taken on site. For remote monitoring, see the R1 wireless crackmeter.

How often should the G1+ gauge be read?

There is no absolute rule: the reading frequency should be agreed with the professional monitoring the building, depending on the context and the level of risk. To observe seasonal variations, particularly with clay shrinkage and swelling, one reading per season is a bare minimum; more frequent readings, for example monthly, give a more detailed picture of how the crack is changing.