A reference mark configuration for an interferometric miniature grating encoder readhead using fiber optic receiver channels is provided. The readhead may include primary fibers that provide reference mark primary signals processed to generate a reference signal with accuracy of approximately 0.2 microns. In some embodiments, a zone grating type reference mark may be embedded in a periodic scale grating, and configured such that it provides strong reference mark primary signals without disrupting periodic incremental measurement signals associated with the periodic scale grating. In one embodiment, the readhead may include secondary fibers used to generate reference mark secondary signals processed to generate a reference signal with accuracy of approximately 20 nanometers.