CEA designs, develops, and manufactures targets, especially equation of state targets, to be experimented on the LMJ (Laser MegaJoule) facility. For this type of target, the dimensional properties of the components must be perfectly known. However, conventional instruments can have limitations in their capabilities to measure thickness and flatness for the thinnest membranes. To overcome this situation, dedicated equipment has been developed using two chromatic confocal probes. This development required studying all sources of measurement errors and implementing specific procedures to reduce them. Applications are shown to demonstrate the capabilities and performances of this instrument.