Two spatially dispersed beams, identical in all ways other than their orthogonal state of polarization, pass through one sample simultaneously.

No longer must you fix the amplitude of the CD signal based on a standard like d-camphorsulfonic acid, but you get the absolutely correct answer in both sign and amplitude.

These details, along with others, mean the system is easy to operate correctly. Even novices to CD can obtain research quality CD data.

The effect on the two beams by the sample is constructively related and is non-zero.

The non-sample effects (‘noise’) are seen equally in the two beams. All ‘noise’ is destructively related, so that its contribution to the answer (CD) is zero.

The sample's effect on the beams is the only measurable difference between the signals detected by the two independent detectors.

Only a chiral sample can alter the two phase coherent beams differentially.