system
Given the following post, respond as if you're commenting on Reddit:
human
How do laser measuring devices have such high precision?

So I just bought a laser measuring device for around $25.  It seems to read down to 1/16 inch precision.  Now I got curious and did the math to figure out what the round trip time for light to travel 1/16 inch and its around 1.0E-11 second.  So what I am wondering is, how is that even possible to have a micro processor time something that fast.  The fastest processor speed that I can find has a clock speed of around 8Ghz.  Even if the cheapo components in my $25 laser measure is actually hitting those kind of speeds, the light would travel about 2 inches in one clock cycle, which would mean it could count in inches, not sixteenths.  The math says it would need to be counting up around 1800Ghz to count with 1/16" precision.  (a 1/16" distance equates to a 1/8" round trip, and a 900Ghz clock will have a 1/8" round trip per tick, but your precision is half your sampling speed, so you need at least double that, right? so 1800Ghz)

 Is there some other principle going on than simply timing the return trip of the light?  The fastest transistors that I can find are in the 300Ghz range.
gpt
For the type of range finder you're using (and not just you, but whenever you want to use a range finder to find short distances) they don't use time of flight. Instead, they send out laser light whose frequency is sinusoidal modulated. What that means is, there is a center frequency (say, ~400 THz is it's red light) and what it does is ramp up the frequency (say, to 410 THz), then drops it down to 390 THz, and then back again. It is easy to modulate the frequency very rapidly, and just as importantly, very consistently in time.  The laser range finder then knows what frequency it is currently sending, and measures what frequency it gets back, and by knowing the difference in what they're currently sending and what they received, it can calculate the time of flight. 

You might think this method is better than time of flight, and should be what is used always. But, these have a limitation. There are range ambiguities in measuring distance this way, because any distance which is d + 2c/T where c is the speed of light and T is the period of the oscillation will measure as the same distance. That's why your laser range finder has a shorter maximum range than a laser range finder which directly uses time of flight to measure longer distances.