Thank you Stevenmac. Attached is spline.doc which was renamed from spline.7z.
The item is in green. Have tried every which way to change the width to no avail. I cut and pasted this into another document and it appeared to work, but not in this one. Any advice gratefully received.
You might not be aware that your 'curve' is actually a multi-segment polyline, and not a spline or fitted line? It only looks curved because it's made up of 30+ straight lines (double left-click it and see for yourself).
Delete it and draw it again with the right tool if need be... however that still leaves the puzzle of why entering in a new line thickness doesn't actually change the polyline thickness.
Are you aware your drawing is set to a precision of "1. mm". If you want a line 0.05mm thick you need to go into:
TOOLS > DRAWING OPTIONS > UNITS > LENGTH > DECIMAL PRECISION > change from 1. to 0.01