Methods and apparatus for normalizing path length in an optical system for non-invasive glucose concentration. A method arrangement includes providing an optical energy source spaced from a first photo-detector by a sensing area transmitting energy from the optical energy source onto the first photo-detector storing a first reading corresponding to the light intensity observed by the first photo-detector subsequently, introducing a container of solution including an optically active substance into the sampling area transmitting energy from the optical energy source through the container in the sampling area and onto the first photo-detector storing a second reading corresponding to the light intensity observed by the first photo-detector determining a ratio of the first reading to the second reading and determining a path length L by computing L=ln(ratio)/μ where μ is an absorption constant of the optical energy in the solution and container. Additional arrangements are disclosed.
