Ruler Measurements Research Articles

A modular system for detecting and displaying plethysmographic blood volume pulse amplitude.

ABSTRACTA modular system for detecting and displaying the maximum amplitude of a plethysmographic blood volume pulse is described. By utilizing a peak detector and supporting logic, the height of the pulse wave for each cardiac cycle is displayed as an analogue step function similar in appearance to the output of a cardiotachometer. This output is simpler and faster to quantify than the typical hand‐scoring of blood volume pulse amplitude and is easily adaptable as a feedback medium for pulse wave information. The validity of the new method was ascertained by comparing its output with trough to peak ruler measurements of blood volume pulse during a variety of events. For each stimulus condition correlations between the two methods of scoring ranged from r= .85 to .99 with an average of r = .93 while within subjects correlations ranged from r= .87 to .99 with an average of r= .95.

Echelle Calibration and Wavelength Calculation

Two methods for calibration and wavelength calculation for echelle spectrograms are discussed. The rough method employing ruler measurements on photographic enlargements has an accuracy of about 1 in 105. The accurate method using comparator measurements of Th standard lines and a computer routine has given an accuracy of 2 in 107 and promises greater precision for spectrograms obtained with modern echelle gratings.

X-Ray Determination of Calcite-Dolomite: an Evaluation

ABSTRACT The observation that X-ray methods currently in use for determination of and dolomite in rocks and sediments often give inconsistent results led us to structure an experiment to evaluate their relative accuracy. Three dolomite standards were selected from which 33 mixtures (11 each) of and dolomite were prepared in triplicate (99 total). The intensities of the major and dolomite reflections of each slide were measured by four methods: by fixed-time count on the peak maximum, integral count of a fixed interval across the peak, ruler measurement of peak height and planimeter measurement of peak area. The parameter dolomite/dolomite plus calcite was computed for each diffraction pattern. A curve of best-fit and the standard error of this parameter, as a function of weight percent dolomite, were computed for various combinations of individual and average data to determine the relative accuracy of the several types of intensity measures. Results of previous investigators were compared with our data to estimate their relative precision. It is concluded that X-ray peak-height (fixed time) intensity measurement provides the most rapid and precise procedure for determination of and dolomite. Composite data for all types of measurement yield a calibration curve which gives results in terms of weight percent dolomite of about ±6 at the 95% confidence level. Its true accuracy is probably better. Replicate analysis of unknowns yield mean values with standard deviations of about 3, expressed as percent dolomite. Most of the curves presented by prior investigators compare well with ours; that is, they lie within our documented confidence interval, and data derived from them can probably be considered reliable within the limits of accuracy established by this study.

Legislation and Correlation

Purpose: The purpose of this study was to determine the clinical setting where errors in measurements of muscle position during strabismus surgery made by the Scott curved ruler or by calipers become important and to characterize the magnitude of those errors. Methods: Geometric analysis was used to determine the measurement error between true arc lengths of 3.0 to 20.0 mm versus Scott curved ruler measurements and caliper measurements for axial lengths ranging from 18 to 30 mm. Results: For measurements less than 9.0 mm, neither the Scott curved ruler nor calipers had any clinically important measurement error for any axial length. For axial lengths substantially smaller than 21 mm or larger than 24 mm, the Scott curved ruler, although more accurate than calipers, caused clinically important measurement errors with arc length measurements as small as 12 mm in very small eyes and 14 mm in large eyes. For axial lengths of 30 mm or more, both calipers and the Scott curved ruler had similar accuracy for measuring long arc lengths. Conclusions: Both the Scott curved ruler and calipers are accurate in measuring arc lengths 9.0 mm or less. For longer arc length measurements, accuracy becomes dependent on axial length. The Scott curved ruler, although substantially more accurate than calipers for most common axial lengths, can introduce clinically important measurement errors when measuring arc lengths as small as 12 mm. Axial length should be considered when measuring muscle position during strabismus surgery. (J AAPOS 1999;3:18-25)