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An extension ruler intended for symmetry measurements of vehicles, having a built in measuring device for the extension of the ruler and transfer of data or figures to a display. The measuring device includes a tape extending from one end of the ruler to the other end where the tape is wound on a dr

An extension ruler intended for symmetry measurements of vehicles, having a built in measuring device for the extension of the ruler and transfer of data or figures to a display. The measuring device includes a tape extending from one end of the ruler to the other end where the tape is wound on a drum spring biased in the winding direction, which drum is provided with teeth and that the passage of these is detected and counted by a light source and a photo diode and that the drum rotation detected in this way is used to provide a measure of the extending of the ruler.

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1. An extension ruler for symmetry measurements of vehicles and for transfer of data or figures to a displaywherein the extension ruler comprises a tape extending from one end of the ruler to the other end where the tape is wound on a drum spring biased in the winding direction, which drum is provid

1. An extension ruler for symmetry measurements of vehicles and for transfer of data or figures to a displaywherein the extension ruler comprises a tape extending from one end of the ruler to the other end where the tape is wound on a drum spring biased in the winding direction, which drum is provided with teeth and that the passage of these is detected and counted by means of a light source and a photo diode and that the drum rotation detected in this way is used to provide a measure of the extending of the ruler. 2. The extension ruler according to claim 1, wherein the spring bias is achieved by a band wound on the same drum as the tape and fastened in a pull spring. 3. The extension ruler according to claim 2, wherein the band is wound onto a part of the drum that has a smaller diameter than the one where the tape is wound. 4. The extension ruler according to claim 1, wherein? the changing diameter of the tape when wound is taken into consideration before the measured values are presented on the display. 5. The extension ruler according to claim 1, and further comprising a spirit level arranged pivotable in one end and adjustable in the other end, said spirit level is able to swivel around a vertical axis between two positions 180° apart. 6. The extension ruler according to claim 5, wherein the spirit level is arranged on the top of the ruler. 7. The extension ruler according to claim 5, wherein the spirit level is arranged on the side of the ruler. 8. The extension ruler according to claim 1, wherein the ruler in the end opposite to the display provided end is provided with a magnetic fastening means including a conical part that is connected to the ruler and that around the conical part a displaceable magnet is arranged lightly spring biased away from the tip of the conical part, and that the magnetic force is greater than the spring bias. 9. The extension ruler according to claim 1, wherein the display is arranged in one end of the ruler, in particular in the end with the measure mandrel. 10. The extension ruler according to claim 8, wherein the conical part is articulated on a ball so as to be essentially level with a hole in said vehicle.