An array chip useful for biochemical assays is provided wherein the chip includes a field region arranged with attachment sites according to a first pitch and at least one track region having a one-dimensional spot pattern arranged according to a second pitch that is less dense and is a non-integer multiple of the first pitch so that one-dimensional Moiré averaging may be applied in the track region, thereby to attain alignment of the chip to the optical instrumentation with a higher density of attachment sites.