Here’s looking at you, kid. Or maybe not…

“CGM monitors display “trace” graphs, a plot of recent CGM readings. It is a map of your recent blood sugar river. And just like glancing at a wrist watch tells you the time, glancing at the CGM trace tells you the context of your blood sugar.”

--Beyond Fingersticks


The new Dex G4 reminds me of Times Square on New Year’s Eve. It’s a crowded place. The receiver screen has a lot of data squeezed into it, and frankly, I really don’t like the layout all that much. Not that I have any practical suggestions, but I’m pretty good at bitching about what I don’t like, so I’m just going to have to go with my strengths today.

The G4’s receiver’s screen is one and three-quarter inch left to right, and one and a quarter inch top to bottom. That’s actually very close in size to the Seven Plus’s screen size. Both devices feature an x/y type of graph, with changes in time displayed horizontally, and changes in blood sugar levels displayed vertically. Every five minutes a dot is added to the graph. Lots of dots make up a trace line that shows where your blood sugar is, where it was a while ago, where it was a while before that, and so on. The shape of the line gives you a good clue as to how fast your sugar is changing. Flat lines mean not much is going on; while sharp ups and downs indicate rocky going.

In addition to the graph itself, the G4 receiver screen displays the telemetry status of the transmitter, the battery status of the receiver, the current blood sugar (or more correctly, the current sensor glucose reading), a trend arrow that shows the relative speed and direction of recent changes in blood sugar, and a blank spot for urgent messages—like calibrate now, or I can’t find your sensor.

The Seven Plus also displayed all this info, plus one other tidbit. So which does a better job? The old girl or the new girl?

Ummmm…. Neither? There are things I like better about the old screen and things that I like better about the new screen. And there are things I don’t like about either screen.

Note: for clarity, I stole these image from the Dexcom website. The shiny surface of the receivers makes shooting them in the wild quite the trick!

There are major differences between how the new and old screens are laid out. On the G4 the x/y graph extends fully from right to left, and the icons that deal with the receiver status are displayed on a small ribbon along the top. This gives us a slightly more rectangular glucose graph than the older model, causing the image to be stretched out a hair. Slopes will appear ever more slightly gentle than they did on the Seven. By comparison, on the older Seven, the graph extended fully top to bottom instead, and the receiver status icons were displayed on the right-hand side of the screen.

Speaking of the graph portion of the screen, there are two major changes in how it’s displayed on the G4, compared to the Seven. The first is the location of the blood glucose scale. Pretty much every x/y graph in history since Professor Euclid in ancient Alexandria had the vertical scale on the left. A convention that became a tradition. The G4 breaks with this tradition and moves the scale to the right side. Why? Well, it’s actually more user-friendly for a CGM monitor. A CGM trace line (or row of dots) travels from left to right. The left end of the trace line shows the oldest information. The right end shows the newest reading. It looks weird at first, but it makes sense to have the glucose scale next to our latest readings. I just don’t know what to make of that; we d-folks aren’t used to medical devices that make sense!

The other significant change in the graph is the G4’s addition of a time index across the bottom. The Seven just had hash marks to signify hours. The new one has the actual time of the readings. You still can’t scroll back across the old data like you can with Med-T CGMs, so I’m not sure how much use this is to us. And sorely missing from the G4 is the Seven’s label of which of the five glucose graphs you’re looking at. The Seven labels each graph clearly: 1 hour, three hour, six hour, etc. I actually find the loss of this tidbit of info from the new G4 to be highly annoying, and the way the time scale works (always three readouts on each reporting screen, with a progressively larger span between the numbers, rather than adding more numbers to the bottom) is no help in this regard. Frankly, it takes some brain power to figure out if I’m looking at the six-hour screen or the twelve-hour screen, and I don’t really have any brain power, or time, to spare.

New devices should make life easier, not harder, damn it.

Going back to the display of the receiver status icons, I can see why any designer might think the Seven was wasting precious screen space by using up nearly a quarter of the right hand side of the screen with the data that relates to receiver status. But I find the G4’s data ribbon along the top overly small, and overly crowded. The telemetry icon and battery status are right on top of each other. On the real machine, they actually touch (the image from the Dexcom website is making it look better than it looks in the real world).

And hey, and what the fuck happened to the current time? I used my Dex Seven as a back-up watch. Why didn’t they put the time on the G4 anywhere? Oh. Wait. There it is. Hidden waaaaaaaay down in the far right-hand bottom corner, almost invisibly small. You can mistake it for part of the time scale.

Both devices suffer from wasted space in the hyperglycemia portion of the graph. Hopefully, most of us don’t really spend much time above 300 mg/dL, so the top quarter of the graph is blank space most of the time. It’s too bad that space can’t be used to display current glucose level and trend arrows largely when the landscape isn’t in use.

Another major difference between the old Seven and the new G4 is purely one of aesthetics. Or maybe not. In this case, fashion has an impact on function. The old Seven’s screen was black on white. The new G4’s is white on black, what printers call a reversal. Well, actually the old screen was more of a pale blue-grey background with dark grey writing. The new one is black background with mainly white writing and some use of color, which I’ll talk more about tomorrow. The G4 is prettier, but hard to read in bright light. Did I say hard? Actually, in some cases it’s impossible, especially if you’re wearing sunglasses.

Now at night, I like the G4 better in some ways and worse in other ways. A nocturnal CGM check with a G4 is not hard on the eyes. So that’s nice. But I also used to use my Seven as a midnight flashlight. I’d use it for lighting up a pitch-dark fingerstick (I wish all meters had test strip port lights like the Flash meters). Or: Oh crap, I just dropped a test strip on the floor, can I find it? Or: What is that cat up to now? G4 doesn’t cast enough light to use as a flashlight or to signal a train that the bridge is out. Hey, it could happen.

Lastly, I need to talk about the dots. There are two ways to display data on an x/y graph. Each data point can stand alone, or you can just connect the dots into a line that’s sometimes called a trace.

Both old and new Dexs use dots. Sorry. I don’t like dots. I like lines instead. I know dots are more scientifically accurate, and all of that. But I prefer lines. They look cleaner and make it faster to interpret the information being displayed, which is the whole point. With a line there’s nothing to slow down the eye or the mind. It’s the direction and flow that matter in CGM. The collective movement of sugar. The aggregate picture. Individual data points are meaningless. The less we obsesses over individual numbers, individual readings, the better we do with CGM. To me, dots harken back to the bad old days of fingersticks where we tried to control our diabetes by looking a snap-shots, brief moments in time, not the real life ebb and flow of our blood sugar as it really is.

That said, the G4’s new dots, for some reason, are more appealing that the old Seven’s dots were. I think it’s because they’re cleaner and smaller. Maybe the spacing is better, too. Oh, and the old dots on the Seven are actually little crosses. The new ones are perfect little circles that look like stars in the night sky—forming constellations of your health. Very appealing as dots go. It also probably helps that with the improved transmitter range, there are less missing dots. On an old Dex Seven, not only did you have these funky crosses, but there were always some missing. With the G4, I’ve yet to lose a single data point—knock on wood. So my closely spaced dots are more line-like.

But I still like lines better.

So there you have it. Crowded. Colorful. Black with city lights. The G4’s monitor screen is very much like Time’s Square, indeed.

But unlike the new year, I just can’t decide whether to celebrate the new G4’s screen or not.