[Disable new point when single value is returned]

In the doc, under refresh parameter it states

If the command returns a single value per each series, the chart will add a
new point to the end. Otherwise, the whole chart data is replaced with the new
data.

 I'm doing some analysis on the frequency of distinct live generated system alerts that are logged into a database, and sometimes my sql query will come back with only 1 value, and that's normal, however I don't want it to scroll and create new points in my bar graph, but rather update. Is there a way to disable this behavior while still using refresh?

[Changing chart background when falls out of threshold]

I'm a newb, and i'm trying to set the background color of a chart so that it changes if the value being graphed falls out of baseline

#--file foo.ps1 

$backcolor = 'Orange' 

$obj = new-object System.Object 

add-member -inputobject $obj -membertype NoteProperty -Name backcolor -value $backcolor

$obj

#--file launch.ps1

.\foo.ps1 | out-chart -values currentvalue -template foochart -PlotAreaColor {$_.backcolor}

It's throwing a WARNING: $_backcolor is not a valid value for Int32 when run .\launch.ps1

Thanks,

-Phil