Hi Pat, many thanks for the above.
Looking into this, it does appear that I have managed to set my user origin as something other than 0,0. You can apparently tell this by the little crosshair being yellow instead of grey according to this: http://app-help.vectorworks.net/2018/eng/VW2018_Guide/Setup/Setting_the_User_Origin.htm
Do you know if there will be any sequential problems encountered if I 'reset' the origin back to 0,0? Or am I sort of stuck with this for now if I have viewports on sheets etc?
Thanks again.
M