# realtime stripchart $Hz Hz

 package require Tk
 package require BLT
 namespace import blt::*

 # vector and stripchart are blt components.
 # if you have a vector v, you can update it in realtime with
 # v set $list

 # init the vectors to a fixed size.

 set Hz 200

 vector create xvec($Hz) y1vec($Hz) y2vec($Hz)

 # fill xvec with 0 .. $Hz-1

 xvec seq 0 [expr {$Hz - 1}]

 stripchart .s1 -height 2i -width 8i -bufferelements no
 stripchart .s2 -height 2i -width 8i -bufferelements no

 pack .s1 .s2

 .s1 element create line1 -xdata xvec -ydata y1vec -symbol none
 .s2 element create line2 -xdata xvec -ydata y2vec -symbol none -color red

 # update $Hz values with random data once per second

 proc proc1sec {} {

        # this can be done more concisely with vector random,
        # but if you need to fill a vector from scalar calculations,
        # do it this way:

        for {set i 0} {$i < $::Hz} {incr i} {
                lappend y1list [expr {rand()}]
                lappend y2list [expr {rand()}]
        }
        y1vec set $y1list
        y2vec set $y2list

        after 1000 proc1sec
 }

 proc1sec