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International Commission on Irrigation & Drainage Commission Interationale des Irrigation et du Drainage

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Multilingual Technical Dictionary (MTD)

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Term No.

Term Name/Term Description

Action

20

An error caused by the inability of the observer to perceive dimensional values exactly. If the personal error is systematic, it is termed as a personal equation. In some cases it can be largely eliminated by an observing programme rendering half of the observed values too large and half of them too small......

25

Experimental error

In general, any error in an experiment whether due to stochastic variation or bias. More specifically, the expression is used to denote the essential probabilistic variation to be expected under repetition of the experiment and not actual mistakes in the design or avoidable imperfections in technique or computations......

48

1 - A term used to describe regularities of recurrence in an ordered series, sometimes rather vaguely. Although the word `periodic` suggests regularity, this connotation is not normally associated with period. Strictly, the word should relate to a period in a mathematical sense, that is to say, a term u(t) has a period w if u(t+w)=u(t) for all valu.....

49

1 - The reciprocal of 1 minus the probability of the value of an occurrence equal to or less than a certain value. 2 - The mean number of such time units necessary to obtain a value equal to or greater than a certain value. For example, where the interval between observations is a year, a return period of 100 years means that, on the average, in th.....

87

Central tendency

The tendency of quantitative data to cluster round some variate value. The position of some central value is usually determined by one of the measures of location, such as mean, median or mode. The closeness that the values cluster round the central value is measured by one of the measures of dispersion, such as the mean deviation or the standard d.....

94

Percentage frequency

A frequency expressed as a percentage of the total number of members.

97

Percentage distribution

A frequency distribution with the total frequency equated to 100 and the individual class frequencies in proportion to that figure......

121

1 - The degree of scatter shown by observations. It is usually measured as an average deviation about some central value (e.g. mean deviation, standard deviation) or by an order statistic (e.g. quartile deviation, range). 2 - See 1666......

124

Positional measures of dispersion, or Quartiles

Measures defined by a certain position on the scale of cumulative frequency; any two of such positional measures, or quartiles, give an idea of the variability......

126

The set of partition values that divide the total frequency into 100 equal parts.

152

Distribution, hypergeometric

A distribution of a discrete variate generally associated with sampling from a finite population without replacement. The frequency of r `successes` [and n - r `failures`] in a sample of n so drawn from a population of N in which there are Np `successes` and Nq `failures` (p +q =1) is : .....

163

Central limit theorem

A theorem stating that, if repeated samples are drawn from the same population, the variations in the values of the means, standard deviation, etc., are approximately well described by a `normal distribution` (because the distributions of such statistics tend to be approximately `normal`)......

172

Probability paper

A graph paper with the grid along one axis specially ruled so that the distribution function of a specified distribution can be plotted as straight line against the variate as abscissa......

188

Operating-characteristic curve, or OC curve

A curve relating the probability of the same decision (i.e. in the acceptance of an incorrect null hypothesis) to various alternative values of the parameter is called the `operating-characteristic curve`, usually abbreviated to `OC curve`. The OC curve shows how the test or decision procedure operates, regardless of whether that operation is corre.....

222

Operating characteristic in quality control, or OC curve in quality control

A curve showing the probability that a lot (or process) level of a quality would be accepted (or said to be in control), assuming the specified sampling plan is in use, plotted against the possible lot or process qualities. This curve is completely analogous to the operating-characteristic curve (or OC curve) for deciding on null hypothesis (See 18.....

258

Period of cycle, Duration of cycle, or Periodicity

In a less exact sense, the intercept along the abscissa (i.e. time in a time series) of an identical phase of cyclic or periodic movements, e.g. the time interval between the peaks or troughs......

260

1 - Strictly the period, as in a time series, for a value to return to the same value. More generally, the average time interval within which a given event will be equalled or exceeded. 2 - See 49 and 7963......

272

Periodic variations

The recurrent pattern of change within the period that results from the operation of forces connected with the period or custom at different times of the period. When connected with the climate or season, these variations are referred to as `seasonal variations`......

312

Perspective projection

The representation of an object on a plane or curved surface as it appears to the eye.

313

Linear perspective

Perspective projection by means of which a true picture of an object is reduced upon a surface anywhere in space from the actual dimensions of the object, as given in a suitably chosen orthographic projection......

314

Parallel perspective, or One-point perspective

Perspective wherein the principal lines of the picture are either parallel or perpendicular to the picture plane.

315

Angular perspective, or Two-point perspective

Perspective where some of the principal lines are oblique and some are not.

316

Oblique perspective, or Three-point perspective

Perspective where all the principal lines are oblique.

317

Diagonal perspective

Angular perspective when the oblique lines make an angle of 45o with the picture plane.

318

Panoramic perspective, Curvilinear perspective, or Cylindri-cal perspec-tive

Perspective when the picture is made on a concave cylindrical surface as in a panorama.

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