Normal Limits

Graph minimum and maximum

Enter the minimum and maximum values that will be shown on the graph. If the Graph Mode is set to NATURAL LOG (Ln), the minimum value must be greater than 0. If you use the short cut method (left double-click or F3) to obtain the maximum value, it will be adjusted to ensure there is an integer number of bins.

End first bin

Enter a numeric value to define the end of the first bin (data range) on the display. Your entry should be based on knowledge of the input data set.

Due to problems with detection limits or with highly skewed distributions, a very large number of values may end up in the first bin on the display. By defining the value for the end of the first bin separately from the boundaries for subsequent bins (data ranges), you can ensure the graph is not distorted.

As a guide to the location of the end of the first bin you can use a value of (Mean - (3 x SD)). Where SD is the standard deviation of the data set.

Bin size

Bin size defines the interval between successive increments on the graph. If, for example, the bin size is set to 0.1, (with the first bin ending at 0.05) the boundaries will be at 0.15, 0.25, 0.35 and so on.

Choose the Bin size so that it maximises the significance of the data. Too large a bin size will result in few bins with very large differences between them. Too small a Bin size will result in bins not being adequately represented (under sampled) giving a “spiky” looking histogram.

As a guide, the histogram should have bins equal to about (0.25 x SD). Where SD is the standard deviation of the data set.

Up to 500 bins may be defined for a histogram.

Graph increment

Enter the interval between values along the X axis of histograms and cumulative frequency curves, or the Y axis of probability plots. Ticks and labels will be positioned along the axis at this interval.

When in NATURAL LOG (Ln) mode, the values shown on the axes may all be grouped at one end unless Apply to Ln values is selected.