Setting ylim while plotting an 'its' object

Hi,

I have an object 'sat' of class 'its'.
How do I have to set the ylim parameter to change the y Axis limits 
while plotting a time series?

Thanks very much for your help, Marcel

 > class(sat)

[1] "its"
attr(,"package")
[1] "its"

 > range(sat)

[1] -0.5908360386  0.0001541759

 > plot(sat,type="p",pch=3,cex=0.5,ylim=c(-1,0.5))

Error in plot.default(x, y, xaxt = "n", xlab = xlab, axes = axes, 
frame.plot = frame.plot,  :
    formal argument "ylim" matched by multiple actual arguments

 > R.version

         _               
platform i686-pc-linux-gnu
arch     i686            
os       linux-gnu       
system   i686, linux-gnu 
status                   
major    1               
minor    8.1             
year     2003            
month    11              
day      21              
language R               

 >