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</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link=blue vlink=purple><div class=WordSection1><p class=MsoPlainText>>Took your advice to heart and calibrated without helmet. Much better!<o:p></o:p></p><p class=MsoPlainText>My non-surveyor assistants are usually dismayed when I ask them to remove everything!<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Apologies, I misunderstood what you meant by display to the left and right. I think I see what you mean now, the following drawing portrays the issue with a Disto sitting on top of one station, and pointing to another. The two stations are horizontally aligned, but the Disto is pointing down. The angular error will be the angle subtended by the height of the laser beam above the station (3.3 cm or 1.2 cm for my DistoX, depending on orientation). If the error is 2-degrees, then this suggests the distance is 94cm (=3.3cm / tan(2.0)) – that’s a very short leg. At 5m, this error reduces to 0.4-degrees, within the calibration error of the device.<o:p></o:p></p><p class=MsoPlainText><!--[if gte vml 1]><v:shapetype id="_x0000_t75" coordsize="21600,21600" o:spt="75" o:preferrelative="t" path="m@4@5l@4@11@9@11@9@5xe" filled="f" stroked="f">
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</xml><![endif]--><o:p></o:p></p><p class=MsoPlainText>In practice, I find legs of 5m to 8m produce the best surveys – much more than that and it is hard to accurately hit the target station with the laser beam, much less and errors like this “position” error start to get too big. Alternatively, when taking short legs, make sure that the “back” projection of the laser beam is as closely aligned to the station as possible – often easy to do for example when taking a shot from one wall across the passage to the opposite wall. <o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Being aware of this issue should help surveyors choose better station positions, especially for short legs. <o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>The gadget shown in other emails would help, but only in certain circumstance – eg shots along the wall still suffer from this issue. <o:p></o:p></p><p class=MsoPlainText>- Ben<o:p></o:p></p></div></body></html>