One embodiment of the invention includes an MR fluid of improved durability. The invention also relates to the aqueous dispersion obtained, which can be coated onto polymeric substrates made of paper or of regenerated cellulose. The lens unit includes a first entrance surface, a first exit surface, a first reflecting surface, a second entrance surface, a second exit surface, and a second reflecting surface. The delay circuitry comprises a software programmable storage medium and a digitally controllable delay element coupled to the storage medium, the delay element being arranged to control the timing offset in dependence on a delay setting programmed into that storage medium. The redundant data is usable to regenerate at least one of the slices of the packet.