A new telltale is now available for readily monitoring movement of cracks or joints in structures to 1 millimeter (0.040 inch). The telltale simultaneously detects and measures movement in a second direction if such movement should occur. The telltale consists of two plastic plates, on the first of which is printed a set of calibrations. Any movement of a crack or joint over which the telltale is installed will cause cursor lines printed on the second plate to change position relative to the calibrations on the first plate. This change can be recorded periodically by simply copying the position of the cursor relative to the calibrations onto a crack progress chart provided with each telltale.

It is envisaged that this crack progress chart would be kept in the project files. The chart is designed to permit readings of each telltale to be made by an inexperienced member of the staff because all that is required is that the position of the telltale cursor relative to the calibrations be copied onto the chart. The interpretation of the readings may then be made by a professional in his own office. The chart may also be used as documentary evidence in any legal action or insurance claim or used to convince the owner of an adjoining construction site that a building is, or is not, experiencing structural disturbance.