# User talk:Simoncaulton

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Hi Simon, the word "divide" in "Finding out ORGX ORGY" was correct. Why did you change it to "multiply"? --Kay (talk) 11:50, 27 July 2017 (CEST)

- Hi, well I tried it and you have to multiply ORGX/Y by QX/Y to get the correct distance. Dividing it gives you the incorrect (very large) distance. Have a look...I may be wrong...Simoncaulton (talk) 12:07, 27 July 2017 (CEST)

Hi Simon, not sure what you mean by distance? This article is about getting the coordinates of the point on the detector that is closest to the crystal (in practice, if the detector is perpendicular to the beam, this coincides with the direct beam position). In this situation, if MOSFLM tells you that X and Y of the direct beam are (say) 100 mm, then you want to convert this to pixel coordinates (which is what XDS expects). Suppose QX=QY=0.15mm, you'd have to divide 100 mm by 0.15 mm, and arrive at ORGX=ORGY=666.7 . This is why I wrote "divide".

- Yes this makes sense. As we were visualising in Mosflm we actually were converting the XDS pixel coordinates into mm for Mosflm. This is how I read the sentence but I guess the original sentence was for the conversion the other way (mm->px). Simoncaulton (talk) 14:43, 27 July 2017 (CEST)