and N. 6. Jurinski Boston College Chestnut Hill, Massachusetts 02167
I
An Automatic Curve Reading Device
It is customary in science for advances in the research laboratory to filter slowly into common usage in the classroom. The reverse process, in which an educational technique is eventually employed in the research laboratory, is far less common. We present here a demonstration that this process is reversible. Educators have been machine scoring test forms for years. One device commonly used employs an optical scanning unit that senses pencil marks on a paper and records the answer as correct or incorrect according to a pre-defined pattern or key. We have developed a method to use such a machine for reading numerical values from graphical input data. These values can then be employed for any analytical purpose the investigator needs and are in a convenient form for furthur computer usage. The scanning unit employed is a Digitek Model 100 Optical S ~ a n n e r . ~Graphs are prepared on a standard size 8.5 X 11-in. paper having a grid of 48 X 61 blanks or "answers." Additional input information required for interpretation are the scaling factors for the X and Y axes. The program was written in Fortran for use on an IBM 360/40 (256 I< storage) system and should be compatible with any comparable c o m p ~ t e r .Several ~ options have been incorporated into this program to enable maximum versatility. These include inversion of axes, a polynomial fit for expressing the raw data in analytical form, and options of linear or logarithmic axes. The procedure used involves merely tracing the original curve upon the "answer sheet" with a dark pencil and filling in the appropriate answer blanks. Multiple responses in one column are averaged to obtain a single value. The answer key consists of sensing the graphs in four sections, each section covering alternate columns of one half of the graph. Combination of all four readings covers the entire gridwork and will reproduce any single valued curve. The table gives a listing of a test for accuracy of the entire process. The spectral data used were obtained from a Cary 14 graphical output sheet. The measured sample was prepared as an N.B.S. Standard Potassium Chromate ~olution.~Readings were obtained by both computer and manual methods. To obtain a reasonable estimate of the human errors in reading the graph, an average of the readings of a t least ten different observers was used to obtain the wavelengths corresponding to certain specified absorbance values. These
' Present address: Computer Science Dept., Pennsylvania. State University, University Park, Pennsylvania. Digitec Opticsl Scanning Corp., Box 40, Newtown, Penn. Copies of this program and a description of the method me available on request. 'N. B. S. Letter Circular, LG1017, January 1955. 460
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Journal o f Chemical Education
readings, along with the deviations, are compared in the table to the values obtained by the computer. Under the recording conditions employed the spectral range of the table was displayed over 2 in. of graph paper and the typical observer expressed his wavelengths estimates to * 5 A. The average deviation among observers at all wavelengths was found to he *4 while the average deviation between observers and ihe computer at all wavelengths was found to he 1 5 A. It is felt that these deviations are essentially equivalent and that the use of the automatic graphical reading process will not introduce any significant error beyond that which ordinarily exists in the manual reading method. The time required for the entire process would not be in favor of the computer method unless at least one hundred or more data points were to be interpreted and transcribed onto cards for computer processing. The time-saving factor for larger data blocks greatly favors the computer method over the manual one. An optional feature of the program allows one to fit the raw data with a polynomial fit to a maximum of a fifteenth degree fit. The fitting process was applied over the spectral region 2200-3500 A which included one maximum and two minima in the curve. The agreement between the values read directly by the observers and the fitted values was not better than *5% of the true absorbance. This error probably could be reduced by applying the fit over a smaller spectral range. This was not attempted under the present study. For simple curves this fitting subroutine has been found to be accurate to within *0.1%',. The authors would like to thank the Boston College Computer Center and the Office of Testing Services for use of their facilities in support of this project. Comparison of Machine Processed Spectral Dota to Manually Processed Data for Standard Chromate Solution
X
Computer X Observers' (A) 0~)
2525 2.575 2625
2520 2585 2630
9R76
-"L,w
""."
IRP?
Deviations between observers an$ com~uters(A)
+5
--510 -12
-
IAvI 5 . 2
' Based upon average of at least 10 observers.
Deviations among observers1
3.2 4.1 2.7 A 1 =.*
IAv1 3 . 6
