How to Read a Binary Watch

One of the appeals to wearing a binary watch is the cryptic nature of decoding flashing lights into temporal meaning.  The problem, of course, is that if you don’t know how to go about decoding those lights, it’s pretty hard for to use a binary watch as a functional timepiece.  If you’re unfamiliar with how to read a binary watch, hopefully this post will clear that up a bit.

To start off with, binary is a system of counting with only two digits: ones and zeroes (unlike the base ten counting most folks use, which has ten digits 0-9).  Each column in the watch represents a different power of two (which is helpfully printed in white on the circuit board).  To convert the number from binary to decimal, all you have to do is add up the “ones”, which are signified by a lit LED.

For example, take a look at the following sample display:


The first thing to note is that the “T” LED is on, which means that we’re looking at the time (as opposed the date, when the “D” LED is on).  The top row of orange LEDs signifies the hour, and the bottom row of blue LEDs signifies the minute.  For the hours, the 4 and 1 LEDs are on, which means that it’s 4+1=5 o’clock.  For the minutes, the 8, 4, and 2 LEDs are on, so the minutes value is 8+4+2 = 14.  Put this together, and it’s 5:14.  Let’s look at another example:


In this example, the 8 and 1 LEDs are on in the top row, meaning the hour is 8+1=9.  The 32, 8, 2, and 1 LEDs are on in the bottom row, which gives us a minutes of 32+8+2+1=43.  So the time is 9:43.

Note that if the “D” LED were on, the top row would be the month and the bottom row would be the day.  So if we saw something like this:


We would know that the date is June (the 6th month) 19th.

Time Saving Tricks

There are a few tricks I’ve picked up that make the addition much quicker and easier to do.  For one, round numbers are easy numbers.  So if the 32 and 8 LEDs are on, I always add those first, since 32+8+16 is much easier for me to do quickly in my head than 32+16+8.  They both get you to 56, but adding 32 and 8 first gets me there quicker.  This also applies to when the 16 and 4 LEDs are both on, or when the 8 and 2 LEDs are both on.

Another trick is that sometimes subtraction is easier than addition.  For example, let’s see what the watch looks like when it’s 2:31


It would take a non-trivial amount of adding to get the minutes decoded here: 16+8+4+2+1=31.  A quicker way to get there is to notice that everything but 32 is lit up, which means that we have a value of 32-1=31.  For another example, if we had 2:15


We can quickly see that everything to the right of 16 is lit up, so 16-1=15, which is easier to do mentally than 8+4+2+1=15.


If you’ve never worked with binary before, it can take a bit of practice to get to the point where you can decode these numbers on the fly.  After a week or so, though, you will likely be to a point where you can translate the numbers in just a few seconds.  I’ve been wearing mine for about four months now, and as a result I’m at the point where I can read a binary clock about as quickly as I can read an analog wall clock.