Confusing interactions between xinput mapping and xinput set-prop

[malcolm moore]

If I use xinput set-prop to change the calibration matrix ( because I am trying to use a SmartBoard as a second touch screen which are notoriously inaccurate )
I can set the values to whatever I like. So far so good, but then I have to do the xinput --map-to-output to tell the machine where the touch is coming from. This
resets the values I first set. If I do the xinput --map-to-output first the xinput set-prop resets that. How do I do both

Thanks

Mal

OpenSUSE Tumbleweed
KDE Plasma
Intel onboard graphics
Left screen is a ordinary 21 1920x1080 screen
Right screen is a S680 Smartboard
Layout is extended


PS my apologies if this turns up twice. This is my first post and I may have messed up !