Measuring a human hair

In this experiment the goal was to measure the thickness of 's hair 

(the picture is used under his permission :D)

We used his hair as a double slit card in the following setup to observe the wave characteristics of light and from them and the formula y = λLm/d measure his hair thickness.

the y value was obtained from the distance between two continuos node
Measured values were:
y = 12 ± 0.5 mm
λ = 670 ± 20 nm (this value was calculated for the same laser previously in class)
m = 2
L = 1 ± 0.005 m
rearranging the formula we get d = λLm / y = 112 ± 8.5 μm

this number makes sense since the thickness for human hair is between 70 to 190 μm