Possible unwanted behaviour of scale factor?

[Andrew Atkinson]

>
> That's not very helpful in your situation though - measuring the zero
> error with the device would be much more complicated than just using a
> ruler, and likely to introduce as much error as it avoids (I guess the
> zero reading is also affected by the beam travelling through the case
> and any air between the lens and the inside of the case as well as the
> additional distance the box adds behind the device).

Yes it is probably that complicated, did think about it for a while, then
decided the scale factor and offset would be enough
>
> How do you determine the 0.752 scale factor?

Wikipedia, refractive index of water is 1.33, granted at 20C and for 592nm,
neither of which are quiet true, but this was just to show it worked. So if
anyone knows the refractive index of wookey cave water for a distox2, we
can improve.....

Amdrew