Axis 282 Uživatelský manuál stáhnout pdf (Strana 49)

Chapter II-12 — Graphs

II-281

The SetScale operation sets the temperature wave so that its X values span the year 2000. In this example,

the date/time information is in the X values of the wave. X values are always double precision. The wave

itself is not declared double precision because we are storing temperature information, not date/time infor-

mation in the Y values.

Manual Ticks for Date/Time Axes

Just as with regular axes, there are times when Igor’s automatic choices of ticks for date/time axes simply

are not what you want. For these cases, you can use computed manual ticks with date/time axes.

To use computed manual ticks, display the Modify Axis dialog by double-clicking the axis, or by choosing

Modify Axis from the Graph menu. Select the Auto/Man Ticks tab, and choose Computed Manual Ticks

from the menu in that tab. This much is just like computed manual ticks for regular axes (see Manual Ticks

on page II-275).

The Computed Manual Ticks box is somewhat different for a date/time axis:

The first step is to click the Set to Auto Values button. Choose whether you need to enter a just the date, a

date and time or just the time for the canonic tick. This will depend on the range of the data. Choose the

units of the tick increment and the increment.

As an example, you might have data acquired over a period of some months showing data that have a

strong weekly variation. The automatic date/time axis never chooses weeks as the basis for the tick incre-

ment, so you will need to use manual ticks. Here is the graph that we start with (we fixed it up a bit — one

major change was to set the date format for the tick labels to show only two characters for the year, see

Custom Date Formats on page II-279):

And the Computed Manual Ticks box after clicking the Set to Auto Values button, and after setting it up for

weekly ticks with daily minor ticks:

Set the format

for the Canonic

tick entry box.

Choose units for the

Tick increment.

200

150

100

1/11/00 1/21/00 1/31/00

Day

1 2 ... 44 45 46 47 48 49 50 51 52 53 54 ... 79 80

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Axis 282 Uživatelský manuál Strana 49