Personally I think the rules aren't clear. With the rules reference we are clearly told it's ok to premeasure but the the tournament rules come along and sudden make everything a bit murky.
I'm presuming they were added to stop intensional slow play and abuse but they haven't very clearly defined what is and isn't allowed.
We know we can't use multiple rulers or tools at the same time, weather you can use a one of each at the same time I think is still a bit of a grey area depending on how you choose to interpret the rule.
I guess as long as both players agree what they are happy with each other pre measuring at the start then everything is fine.
As a TO my problem is what might be ok to one player might not be with another and I need clear precise rules to be able to back up any decisions I make.