From: Arthur Rowe <Arthur.Rowe@nottingham.ac.uk>
  To  : rasmb@bbri.harvard.edu
  Date: Wed, 2 Jun 1999 12:23:17 GMT0BST

radial step intervals in the XL scanning abs optics

Hi RASMBers !

Trying to do a bit of hard-nosed analysis of data from scanning absorption optics, 
and wanting to have data equi-spaced in r (well - thats nice for all sorts of good, 
sound, numerico-analytical reasons) I was struck by how variable the step size in r 
seemed to be within a given run.

With a nominal set interval of 2 micrometres, for a data set quite typica of many, I 
found the following:

=============================================
STATISTICS FOR FIRST DIFFERENCE IN r:

# Valid numbers       	=   	53
Sum                   	=   	0.1440
Mean                  	=   	2.7170e-3
Variance              	=   	2.1684e-6
Standard deviation    	=   	1.4725e-3
Mean abs. deviation   	=   	1.2374e-3
Skewness              	=   	0.5906
Kurtosis              	=  	-0.8024
Median                	=   	2.0003e-3
Maximum               	=   	6.0000e-3
Minimum               	=   	9.9993e-4
=============================================

In other words, the ACTUAL mean value was 2.72 micrometres, with a standard 
deviation of 1.47 micrometres, and individual values varying between 1 and 6 
micrometres !!!  Oddly enough, the MEDIAN value is almost precisely 2 
micrometres.

 I should say we have our XL-A regularly serviced, and the slit scanning system was 
specifically checked (and its radial calibration) not long ago.

What is the general experience here of XL users ?  Is this just one of those things 
one has to put up with ?

Best wishes to all

Arthur Rowe



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Professor Arthur J Rowe
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University of Nottingham
School of Biological Sciences
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