Many people use the calipers that tiffmaxee (Elise) gave you the link for above. Marje did a science experiment and found that syringe markings can be off by as much as 0.5u. They print the markings on the syringes, but they don't seem to all start at the same place. If you look at 5 syringes and compare them, you'll likely notice the same thing. After she did that many people went to calipers. They are as cheap as $5, and you use them to measure instead of the markings on the syringes. So if you have trouble measuring, or you find your syringes are inconsistent to each other, you might think about calipers.
As far as Marmalade's dose - what a nice cycle during yesterday's day! I think because you aren't able to get night cycle tests, knowing that so many cats have their lowest numbers at night, i'd be a little cautious on increasing the dose - just do it a little bit more slowly so you have more data to rely on, even if it is all in the day cycle. Yes, I think she's bouncing. Which means she might be high for as many as 3 days after yesterday - so mid-day Saturday. She might clear the bounce sooner, too.
Does she have access to food (low carb canned) at night in case she needs it? In your situation, it might be well worth it to have a timed feeder going off every couple of hours during the night. Here's a brief discussion on them - look in this
"Where Can I Find?" post, scroll to the bottom and look for feeders, timed.