Jim - thanks for showing the progression of the glass and adding your explanations - so helpful
I really do get a lot of pleasure seeing the way you apply the paint and mix the colours - so thanks again for that!
The two wineglasses are a really good example of the ellipses and distortions - glad you posted it
Pam - do join us, it's usually enjoyable - and I don't SHOUT!!!!!
Apart from the tip I gave earlier, you can also actually measure from a central line, if that would be easier.
Draw a centre line, mark the levels where you want opening, neck, 'shoulders' and base. Measure equal widths along a horizontal line (much like Jim's example) and then 'join the dots' - even use a ruler for the straight lines.
Where something needs curves - again, either measure and draw a number of reference lines cross or do one side, trace, reverse, and draw over your lines.
I don't think practice studies are ever a waste of time (well, if you don't learn anything then maybe they are!) but practice
is learning to do something you need to learn, not something you already know.
......and again, as Jim says - paint what you see
not what you think you know!