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> Detailed description of G4 gauge

The G4 gauge is intended for measuring variations in the width of cracks and damaged joints in inaccessible parts of structures: cathedral vaulting, tower block parapets, towers, bridges, silos, distant beams etc.


Wall below guttering of the church of St Martin de Lure (25). With the G4 gauge the changes in the joints in the stonework can be assessed from the ground.


Reading the G4 gauge directly is possible from up to 50 metres away, (with binoculars or a surveying instrument)

This gauge is in transparent polycarbonate so as to be inconspicuous.

The dial plate measures 140 X 160 mm and is 24 mm deep.

The arm (20 X 60 mm), which can travel 55 mm, includes a lead and an oblong hole with a knurled screw to take up any play during installation.

A needle movement of 5 minutes on the dial corresponds to a horizontal variation of 2/10th of a mm.

One division of the indicator corresponds to a complete rotation of the needle, i.e. horizontal variation of 2.4 mm.

> Installing the G4 gauge with the protective casing

We recommend installing a protective plastic casing if the gauge is exposed to the weather.
The casing is 33 X 28 X 6 cm; it has a self-adhesive strip around the edge 25 mm wide and 2 holes to ensure ventilation against condensation. During installation, we recommend making a hole at the lowest point of the casing to unable any moisture from infiltration or condensation to escape.


Hôtel d'Assezat in Toulouse (31)

> Installing the G4 gauge on a relatively flat surface


Device for fixing the arm, supplied.












The mismatch between surface A and surface B is of a few millimetres.

> Installing the G4 gauge with double ball joint for a major mismatch


On any kind of structure, as planes A and B are mismatched to a significant extent this may produce 3 dimensional changes.Double ball joint device for fixing the arm. (Please consult us)
A: Plane A , B: Plane B , C: Crack

> Description of the G4+ gauge

The G4+ gauge is designed to measure accurately to 5/100th of a mm changes in a crack or distortion located in an inaccessible part of a structure.
This may be a parapet, a cornice, a tower, a bridge, a silo, a dam, vaulting or any part of a structure showing any form of movement that it is important to examine accurately from a distance, because it is difficult to reach.

Installed by SEMTCAR, Urban District of Rennes

As for the G4, installing the G4+ may be done using a ball joint, or otherwise.

It is possible to take readings directly from up to 20 metres away, and beyond that using binoculars or surveying instruments.

The precision mechanics of the device are sealed in an unobstrusive, transparent, 140 X 210 mm polycarbonate plastic block, 40 mm thick.


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