auto-scaling of stacked charts doesn't work

[Jabson]

Labview 6.1, Win2000. I have a waveform chart with 6 stacked plots. All of the Y-axes are set to auto-scale. They will auto-scale "up", but not "down". Changing the y-axes manually by entering limits with the keyboard, using the zoom tool, or using the "hand" tool, causes autoscaling to suddenly start working again. What's wrong here? Small sample VI attached.

[Jabson]

As a follow-up, it looks like the auto-scaling works if "Loose Fit" is disabled for all the Y-axes (thanks to my NI rep for figuring that out for me). I still think it doesn't work right if Loose Fit is enabled.

[Zvezdana S.]

Jabson,
This is actually an expected behavior with the waveform charts. The autoscale will look at all the values in the array of data, even those that are not visible at the moment on the chart. Then it will autoscale with the respect to the min and max of all values.
Loose fit changes this behavior, so that autoscale looks at only the currently displayed data values.
Loose Fit: When this property is set to TRUE, the end markers on the scale will be rounded to the closest multiple of the increment for the scale. If FALSE, then the end markers will move to the beginning and ending points for the scale. This property only takes effect when Autoscaling is enabled.

Zvezdana S.
National Instruments

[Jabson]

In the example VI I attached, even if you wait for data to completely scroll out of the chart history the plots still do not autoscale. This would also not explain why the autoscaling (as I think it should work) kicks in when you try to adjust the scale manually.

I can't recall ever seeing a version of Labview where the autoscaling depended on values in the chart history but not visible on the screen. Autoscaling has always been just to the visible portion of the data.

[Greg_McKaskle2]

> As a follow-up, it looks like the auto-scaling works if "Loose Fit" is
> disabled for all the Y-axes (thanks to my NI rep for figuring that out
> for me). I still think it doesn't work right if Loose Fit is enabled.
>

I suspect that the problem with Loose Fit is that the chart scales are
small enough that they don't have many inner markers. This may seem
unrelated at first, but the deal is that loose fit loosens the outer
markers to be a multiple of the increment. When your scale goes from 0
to 100 by 10 and has eleven markers, then that means that the
autoscaling will move around as long as it is a multiple of ten. Of
course if the autoscale zooms way in or way out, the increment changes
and that is used for the loosening. On the other
hand when the scale is
small or the font is large, say 0 to 100 by 50, then the zooming happens
in multiples of fifty and the autoscaling is somewhat less responsive,
looser.

As for what happens with the X scale, waveform graphs and charts
consider only the data onscreen for autoscaling. XY graphs look at all
data.

Greg McKaskle