Hello,
Try the following code to move the slider around to get the correct viz.MainWindow.setOrthoOffset() value. On our sx111, around -196 looks just about right.
	Code:
	import viz
viz.go()
viz.add('tankmaze.wrl')
text = viz.addText('Hello World',parent=viz.ORTHO,fontSize=60,align=viz.TEXT_CENTER_CENTER)
viz.link(viz.CenterCenter,text)
slider = viz.addSlider(pos=(0.5,0.1,0))
slider.set(0.5)
def SetOffset(pos):
	offset = vizmat.Interpolate(-400,-100,pos)
	viz.MainWindow.setOrthoOffset( offset )
	print offset
vizact.onslider(slider,SetOffset)
import nvis
hmd = nvis.nvisorSX111()
 Best,
Masaki