Tell-Tales are precision gauges that consist of two plates which overlap for part of their length. The bottom plate is calibrated in millimetres and the top plate is transparent and marked with a hairline cursor in the form of a cross.
They are manufactured in vandal resistant polycarbonate. The coefficient of linear thermal expansion is 7.0 x 10-5cm/cm/ºC for ambient temperatures between -30ºC to +30ºC. They are manufactured to conform to BS EN ISO 9001:2015.
The Tell-Tale is fixed across the crack using screws and plugs and/or adhesive. It can be used across cracks in vertical or horizontal directions on flat surfaces.
The Tell-Tale is preset at zero with transparent tape. The tape is cut after the Tell-Tale is fixed across the crack.
As the crack opens, or closes, the cursor moves relative to the calibration scale. The opening or closing of the crack is then recorded on a crack record sheet.