Hi,
@Boozon , glad you're enjoying libre, it's been a total game changer for many of us.
The graph on the reader can look a bit uppy downy because the screen size is so small.
There's a piece of software which is more useful for detailed analysis:
www.freestylelibre.co.uk/libre/discover/your-data.html
I entered my bolus doses and carb counts and after a week or two it was useful to look over the daily graphs and see which meals worked out best in terms of post-meal peaks - it marks it on the graphs.
That let me work out ratios and a rough and ready pre-bolus time of about 20 mins.
I could then add a few bells and whistles. If I saw from the reader graph I was trending up, I'd lengthen the pre-bolus to give the insulin more time to get to work before hitting it with food, and vice-versa if the graph was already trending down.
And I'd adjust depending on whether the meal was low or high GI.
The software also produces an AGP graph - ambulatory glucose profile. You select a time period, a few weeks or so, and it strips out the top and bottom 10% as outliers, then collates the daily graphs into a single typical day.
That way, rather than trying to assess trends from the daily graphs, it's easier to see recurring trends over a period of time, such as declining during the night, which suggests basal needs tweaked, or post-lunch spikes, which suggests a ratio or timing adjustment.
Once you see a definite recurring trend in the AGP, you can then have a look at the daily graphs for the time of day it's recurring to see if those give any more clues about dosage etc.
Another really useful thing is the Active Insulin Calculator. It's tucked away in the Professional Options, the code to access it is CAA1C. After you set it up, each time you enter a bolus, a gingerbread man will appeae on screen, tap it and it'll tell you how much insulin you've still got on board. It's very useful if you're deciding whether to do an inter-meal correction bolus. If I'm going too high between meals, and I see I've only got 1u IOB, I might reckon that's not enough to bring back down so might do a correction, whereas if there's 5u, I'll leave it.
There's a useful book on kindle which helped me a lot after I got libre, Sugar Surfing, Stephen Ponder. Lot of useful tips on how to interpret cgm graphs. One of his main themes is that diabetes and the action of insulin is so unpredictable that there is no such thing as a reliable fixed ratio, so if a meal is starting to spike you more than it should do, there's nothing wrong with doing a 1 or 2u inter-meal nudge down to keep in range. Or a quick 5g of glucose when you see it trending down to steer it clear long before it gets anywhere near hypo.
Once you've got familiar with libre, many of us have found it useful to add a small transmitter, like blucon or miaomiao, on top of it, which turns it into full on cgm. The transmitter pings a reading every 5 mins to a phone app, xDrip+ for android, or Spike for iPhone. The graphs are way more detailed, and you get hypo/hyper alerts and predictions.
Good luck!