The King Wang solution to the NATO watch strap

I don't know why its taken me so long, but I finally figured it out.... all it took was this WW1 trench watch homage and a new leather strap to work it out.

Readers of my blog will know that I've long derided NATO straps as being (for civilian use) a problem looking to be a solution for. I've likened the whole stupidity of an extra flap under the watch as being akin to wearing tie your self bow tie tied badly, when you're supposed to be at formal black tie evening.

Bringing nothing but bulk behind your watch, puffing it out further from your wrist for no actual benefit (kiddiez who can't actually think will squeal and say "sir sir ... its to prevent watch loss if you break a spring bar", yet any single pass strap will do that) I really don't get why NATO straps are considered "premium".

But as Carl Jung so succinctly put it:

I'm not as polite as Carl so I'll say "... that's why most people are stupid." Which is why this NATO thing persists. People often have no experience, see it as being military or "James Bond" and don't think further than that.

But, wait, today I've discovered the KingWang solution which I will present to you here (and we all know,  King Wang likes to watch).

Firstly if you don't have a 9" wrist the leather NATO just isn't going to work because, not only is there the extra thickness, the bloody buckle that anchors the useless flap gets in the way of allowing the watch to curve around your wrist.

As shown above. This is especially a problem with larger watches on a (does this big watch make my skinny wrist look too much like a chicken leg?) small wrist; such as my 6.5" wrist.

However a little thought allowed me to see a way around this conundrum (I mean apart from the obvious solution of cut that stupid flappy bit off solution; presented here).

Once one thinks like the Ministry of Defence (using military intelligence) we can see the obvious. This cunning lacing style is an optimal solution because it not only protects the watch crystal from being scratched or broken as well as fitting perfectly, but solves the issue of bulk by only having one layer of leather under the watch.

So I present to you the ultimate optimal lacing technique for threading your NATO strap, having it fit and protecting your watch for those too challenged to use a pair of scissors and cut that flap off.

A King Wang solution.

Win Win

All jokes aside, this is the watch on my Green (started as a) NATO and the Red strap (now having had its useless bit cut off) beside it.

The Green one is a very comfortable waxed leather. Each strap was under AU$25. 22mm thickness which of course is not proper NATO either.

The commonly called NATO strap has several written characteristics, and probably many more unwritten characteristics.

The current military specification strap comes in only one colour (Admiralty Grey) and one width (20mm). The hardware specification is chrome plated brass with a recessed buckle to receive the tongue.   Length 280mm, width 20mm, thickness 1.2mm.

It is currently defined in Ministry of Defence, Defence Standard 66-47 as Strap,Wrist Watch.

(source) 

Some other details about the Roche CoaguChek XS

The Roche CoaguChek is pretty much the backbone of my personal self management of my INR. I have on many occasions discussed that I compare it to the lab and often get quite good (less than 0.2INR units) correlation with labs. This is something which is occasionally still debated (particularly on the internet) but which to my mind was put to bed back in 2012 with many comparisons of its accuracy vs that of other systems. So I'll not waste your time and repeat that here.

Determining INR is based on measuring the time taken for "coagulation" to occur.

Note: That's a minefield right there, so lets just leave it simply at: a timer is started and stopped when the machine determines coagulation is "completed" (*according to guidelines like reagent ISI, another rabbit hole for you the curious).

The CoaguChek uses "amperometric electrochemical" methods for determining the time to declare the point of "coagulation" to stop the timer. A good summary of this and other methods is here (link).

So having swept that detail off the table, I wanted to get down to exploring a little bit about the CoaguChek XS system which we can easily see, but may not have noticed (even if you've used one).

First, lets have a quick look at the strips, they are much bigger than the strips used by Blood Glucose monitoring strips. Shown below.

Obviously the strips above are used because I prefer not to risk contaminating them for photography and so you'll see traces of my blood in these images. Note that circular hole in the strip at about the 24mm point. I'll circle back to that.

This video gives a quick walkthrough of the XS. 

As you saw in that video the CoaguChek strips have three layers of plastic, seen in the image below. 

The top printed layer is white, in the middle is a black layer which is used to form the blood capillary tube and then there is a clear base layer (which I'll call the substrate). I can't measure the thickness of the black layer, but I used my trusty digital callipers to measure what I could and thus determine the thickness of black layer. The thicknesses of the strip will tell us about the thickness of the blood channel

• white part is 0.36mm
• the clear base is 0.35mm
• the entire width of the strip 0.89mm

and so thickness of the black strip is 0.18 mm (which is the depth of the blood channel). I could have tried to get a feeler gauge in that overhang, but did it this way instead.

Now we know that Amperometric analysis is used and (from this obscure source) know that the XS system uses a lyophilized reagent (reagent in dried form). The reactive components of this reagent consist of thromboplastin and a peptide substrate. In that above link (here again) chapter 5.3 is of relevance to the CoaguChek XS. But basically the blood needs to flow past the thromboplastin reagent and starting the process. You can see where it goes in and where it ends up in this picture of the underside.

Note that the hole allows the capillary attraction to pull the blood through (from where you placed the blood) across the chemistry, through to the area where the sensing occurs. You can see this below too.

The  hole is needed to allow the blood to flow right through this channel, and I assume that a light  shone through the hole indicates that sufficient blood has now reached the end of the channel. 

You can see clearly below that it is a hole below

So from all of this we see how the blood flows, why you need to put the blood on the top of the strip, or if you use the side (also mentioned in the documentation). From the Roche CoaguChek XS manual:

Exploring the 15 Second rule and outcomes

So, for those who are interested

however, as always I encourage people to not only adhere to that 15 second rule (and myself follow it) but to try as much as possible to treat it as a task that you do with accuracy and reproducibility. Do everything the same just like (say) you were making pottery mugs for sale.

Summary

Basically after watching those videos and reading the above you should know more about:

• how to use your CoaguChek XS device effectively 
• be in a better situation to understand why they make a lot of points again and again in the manual like 15 second rule and application of blood, and preparing your finger for getting a good blood sample
• You should also be able to dismiss any misinformation you may read on the internet (such as how the blood could coagulate clumps could and block the flow)
• from a logical perspective of how the whole system works both physically (the capillary attraction) and the way the machine knows sufficient blood is present.

Knowledge is power and freedom from the anxiety which stems from ignorance.

HTH