More results -0.0551%

EDIT : Funny story, when I first posted this the title was -0.0003% but after looking at it for a few minutes I realized I had in fact moved Ds by 10mm after I did the distance measurement. Clearly accurately measuring distance is going to be the hard and important factor here. I've corrected the numbers below to account for this.


I took extra care to reduce the amount of light hitting Ds by turning the beam off axis. Such that Ch1 (Ds) was 10V/div and Ch2 (Df) was 5V/div. This time I was triggering on Ds at just around first knee as I described in my last post (point A)

40 measurements in total, and I also recorded the required parameters to calculate the refractive index using the NIST tool

Air Pressure :1022 Bar

Temp :13.5 c

Humidity 72 %

Wavelength 532 nm

Giving n and c in air below.

n 1.000281673

c 299708038 m/s

From that I expect the round trip time to be - Yes I remeasured the distance again 

distance 18.2338 m.

expected 6.08385E-08 s

Here are the results.

Average : 60.805 ns

Error : -0.0551 %

Error : 3.3542E-11 ns

Speed : 299873366 m/s

Error : +165327 m/s

I'm going to look at the precision and errors later but just wanted to get this down on the blog. I would expect because the averaged time gives 5sf I can say I'm no worse then -0.0551%