My T:slim and Dexcom Journey: Observations, Questions, Compliments, and Concerns

I’ve been thinking about this all day. I thought maybe I had misunderstood you because a difference in terms— I’ll stop myself from telling you right now which words I may have gotten confused— though it’s tempting to explain it all… Anyway, but then I realized we might actually be saying something different. When you say just a couple of taps to turn Basal-IQ off, you were referring to the actual setting, right? I thought maybe you were also referring to just resuming insulin. It sounds like that is a very easy way to handle it, but I did watch today, and I think I’m doing something a little different. If my Basal-IQ is active and all deliveries have been suspended, and I want to do a bolus for that 35 g of carbs in your example, I resume insulin and enter the bolus. At the next updated sensor reading, I’m suspended again. So it sounds like your method is cleaner in that you don’t miss even a minute of a suspend, but mine might be fine as well in that the only steps you need to take are to resume insulin and enter bolus. Am I understanding this right?

And I’ll just say that my screen was all stripes again after my run today. Boy, would it be nice to be able to look at something like that and realize I need a Basal cut… It’s not that I can’t figure it out based on the persistent lows, but to look at the screen and see all those suspends… it’s just a convincing visual presentation.

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You are completely understanding.

Your method is better.


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No… not what I was looking for at all. Just trying to make sense of everything. :thinking:


Well now I am confused.

In your previous post you showed a complete and total understanding of how this works.

So, now I do not understand this posting?

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@Thomas… and now I’m confused…

What are we talking about here? :grin:

I was worried you thought I was looking for that “your method is better” comment, and I was just trying to let you know I wasn’t saying my method was better but just trying to clarify if, in fact, we were talking about the same thing. The lingo is just different enough that it can make communication on my end a little tricky because I’ve been using different terms for the same stuff for the last year and a half. Just trying to adjust to it all.

What I think is that I’m moving along just fine— I’m just a self-doubter by nature, so my instinct is to worry I don’t actually understand something at first thought that I understand it. Try not to follow whatever I say too closely. It will make you dizzy. :grin:

As I was writing this I got a call from Tandem… just checking in to see how I’m doing, whether or not I’ve got Basal-IQ up and running, and how my cartridge fills are going. That’s amazing. I like this very much.

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Perhaps you are overthinking it.

In my previous post, I was saying that you seem to have perfectly understood the functionality.

There are two different approaches to doing a bolus when the Basal-IQ is active.

Your method is better. It has nothing to do with a contest. Your method simply is better.

The fact that you described both processes, understood the mechanics and implications of both, tried the one out, had success, etc, etc, etc, clearly shows you have a very good understanding of what is going on.

Don’t self-doubt. I am not a kumbaya huggy fuzzy smoke blowing person. If you were doing something technically wrong on the pump, I would say it.

Roll with it. You are doing great.

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My method is different. In the case of the extended bolus, which I haven’t done yet, yours would be preferred. Mine would be a disaster. I haven’t had a reason to do an extended bolus yet as I’m still going some manual injections, but I’ll be giving those a shot soon enough.

No. Most certainly not. :grin:

Thanks for the pep talk. Off to run and work on not overthinking things. :grin:

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Different scenario.

Extended Bolus (which as you say you have not done yet)…

… when taken in conjunction with Basal-IQ is an entirely different operation from a regular bolus.

Don’t think of Extended Bolus with Basal-IQ to be a slight twist of Bolus with Basal-IQ. Think of it as an entirely different operation. When we are doing an Extended Bolus with Basal-IQ also running then I consider this to break down into two different cases depending on the current BG at the time of the extended bolus.

Case 1: Extended Bolus with Basal-IQ when BG is 80 which is my “Food with Protein/Fat” case.
Case 2: Extended Bolus with Basal-IQ when BG is 250 which is my “High BG” case.

In Case 1, the Basal-IQ rules kind of work against you so you have to fight it a bit.
In Case 2, the Basal-IQ rules work in your favor and give you increased flexibility.

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Works in your favor? Do you mean it actually helps you, or do you just mean that that high BG prevents it from knocking itself out?

I can see why BG of 80 with an extended bolus and with Basal IQ activated is a tough combination. That’s Auto Mode. You are where you want to be, but being there makes your pump want to slow down your insulin. Obviously, in the case of the T:slim, it would just knock out the extended bolus anyway. I’m having a tougher time with the 250 though— unless you just mean that being at that BG takes care of the problem on its own…

Another question. My mornings can be awful. I have some of my worst crashes in the morning with the trying to get the kids ready. If I don’t do quite enough insulin, I can stay too high for hours. So mornings are tough. This morning, I hit a long suspend, but I left it in place. I was so low I couldn’t see, and I needed to be able to operate the car. I figured I would just take my chances on a big rebound. I have all of my alarms on, and my BG is hanging around 40, and my sensor is reading a 45. I had been suspended for almost an hour at this point— and then my pump alerted me that it was resuming insulin.

I actually love this, but I know with everything going on and being as low as I was, I may have misunderstood what had happened. I don’t think the pump will resume insulin under a 70 until you’ve reached 2 hours, right?? I haven’t had the chance yet to read about clearing alarms, but I am thinking that may have just been an old alarm I hadn’t seen yet?? Can it resume insulin at a 45??

It resumes the first time your sensor reading increases at all, so it can resume insulin at a 45 if you had been at a 44 before. This is why it doesn’t tend to give me bad rebounds, but you do need to keep an eye on things like this. Usually if I’m that low for that long I will have a bit of carbs because it can be harder for Basal IQ to overcome stuff like that


Oooh, I love this. I was hoping that’s what it had done, but I thought it would remain suspended until above a 70. I was not too fond of that, but I was willing to see how it did.

Oh, I am absolutely treating with carbs at those numbers. Sometimes I’m doing insulin, too. When I’m around a 70, I’d be happy to let it try to sort me out, but under that I’d probably just take a small amount of carbs to carry some of the weight. I love the quick suspends, and I feel they work well with little carb boosts. I’d like to avoid the long suspends at all costs— though this morning’s left me at an 88 when it was all done. Can’t hate that.


Yeah… So… True there is the Basal-IQ rule about 70. There is some debate about exactly what that means.

Although it may feel good to delve into that aspect and pick it apart and dissect it and discuss it to death and then go back and do it again…

My suggestion is to pretend that the rule about 70 does not even exist. I find simply focusing on the other two rules:
(my paraphrase)
#1 Insulin suspend on prediction of under BG 80 within 30 minutes
#2 Insulin resume as soon as first cgm data point shows a rise

The third rule about the max two hours out of two and a half hours is very real but if you hit this then it generally means something is wrong. This is a safety net rule and not mean to be activated under normal operating conditions.

Anyway, the above (paraphrase) two rules give me all the understanding of the workings of the algorithm that I need. On an observational basis, I actually have not seen evidence for the workings of the 70 rule. I totally trust what Tandem says so I have no doubt it is in there but it could be a contingency or fallback rule or maybe something that kicks in under limited circumstances or perhaps Tandem simply did a poor job of describing the “70 rule”.

I ignore the “70 rule” like it is not there.

How does Basal-IQ Technology work?

Basal-IQ Technology uses a simple linear regression algorithm that predicts glucose levels 30 minutes ahead based on 3 of the last 4 last consecutive CGM readings. If the glucose level is predicted to be less than 80 mg/dL, or if a CGM reading falls below 70 mg/dL, insulin delivery is suspended. Insulin delivery resumes as soon as sensor glucose values begin to rise. Insulin may be suspended for a minimum of 5 minutes and a maximum of 2 hours within a 2.5-hour rolling window.


Oh good. A mystery. I was afraid the X2 would be without any. Almost everything was a mystery with the 670– and it left me a little spoiled. :grin: This is very interesting to me, and I would love to look at it closer… down the road. For now, I’ll just keep feeling happy when I do see it resume under 70. :grin:

Arrows… I used to laugh at the arrows on the Guardian. It’s not that they were just wrong, it’s that they were so delayed as to appear to be wrong. Making them wrong. I could be at a 75 and rising really fast, but my Guardian might just now be reflecting a 55 with two arrows down. I mention this because I’m curious if the arrows are at all indicative of anything… Wait— I was actually asking because the other day I was suspended at a 121 with a side arrow, and I got nervous. (That’s that old trauma, but it’s fading). That was probably a 121 with a predicted drop to below 80 within 30 minutes, right? The arrow should just be ignored?

I know you might think I’m over analyzing, but I swear I’m not spending any amount of time at all during the day doing this. I’m making a few mental notes here and there and just doing what I think is necessary to get a good number. I’m asking you only because there’s a chance you might know— a good chance you might know— and because it saves me picking up the manual and getting lost in it. I don’t think I need the manual right now. I think I need a few quick explanations and then to just see how it looks live.

And now I’ll prove myself a liar by saying that rule might make perfect sense— if you use an alternative meaning of “falls”— if your CGM reading is falling, and not rising under 70 (rather than falls under 70, which makes it sound like as long it is any value under 70 at all), then it suspends. So just a continued trend downward that is taking place below 70– no matter at what rate. Then this part:

Is as clear as day— as soon as there’s a rise, despite at what value, the insulin resumes. It might just be a case of a poorly written rule rather than an inconsistent one.

And now I’ll go back to not worrying about it and feeling happy. :smiley:

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I love the Dexcom.

I hate the Arrows.

I pay them no attention.

I may have figured out the stupid algorithm they use but I just pretend like the arrows are not there.

Stupid arrows. Stupid algorithm to point the arrows.

See - You are picking this up super fast. It is the huge difference between somebody new to pumps, new to insulin, new to diabetes vs somebody like yourself who has a vast amount of experience with everything except this particular piece of technology. You are using all your knowledge and experience super to transition over. If in doubt - go with it. You really understand all this.



I can’t figure out why Dexcom doesn’t show the actual change between the last data point and the current one, which is the type of useful informations the arrows wish they could convey. This is why I love stuff like Nightscout/Sugarmate, because they’ll tell me if that down arrow is because I’m moving at a rate of -2 or a -14 without me having to look carefully at the data points to figure it out (if you even can, with the Dexcom data smoothing)


I totally agree. I have my private ideas (oops - you already called it out - lol - yeah, Dexcom smoothing) on why not. In any event, I like this little app:

It shows the difference between the readings which is nice. (No Dexcom smoothing here.) I can keep it open in a corner of the computer so it is pretty convenient.


I can’t even remember if this was anyone else’s question or just mine, but I found in the manual what Basal-IQ does when there is no sensor reading, and this just confirms it. It will continue to remain in place for 15 minutes because of the fact it uses 3 of the last 4 readings. So those 3 readings can carry it 15 minutes, but if it doesn’t pick up a reading at that point, then the Basal-IQ turns off. Maybe. If you agree with that @Thomas and @glitzabetes. :grin:

Now for some random questions:

-What’s Dexcom smoothing?
-What’s the Costco stuff all about? And does it have anything to do with insurance??
-What’s the best way to look at your graphs and data? And should I bother getting I:connect set up?
-And, last— is it possible to extend a transmitter? A fairly tech-savvy friend thought she could extend hers, but I didn’t know that was possible…

Hope you all are having a splendid weekend!

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Somewhere up there deep in the thread is a mention of a waterproof bag for use during water play. I’ve worn it with both the 670G and t:slim. It’s not the easiest to get on the first couple of times, but it does get easier, and it does keep the pump dry. Just posting it because I said I would…

And it’s the “wire-out electronics” one.


I know people are really excited about the Costco thing.

Right now the Dexcom G6 Transmitters direct from Dexcom cash price cost about $2.22 per day.
The Dexcom G6 Sensors direct from Dexcom cash price cost about $10 per day.

Pricing may vary.

The Costco thing is no insurance / cash from Costco only in regard to G6 Transmitter.

I would have a hard time getting excited about only the transmitter.
If it was sensors on the other hand for a huge discount? Yeah - that would be exciting for a cash customer.

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So no point in stocking up on transmitters?? Don’t think I’m crazy… I just always get excited when I can get something that doesn’t require going through insurance. :woman_shrugging: