A rotation angle encoder apparatus, comprising: a first configuration comprising: a first light source that generates a first light bar; a first light detector to detect the first light bar from the first light source; and a first pinion fixed on a rotatable shaft, wherein: the first pinion comprises a plurality of teeth and a plurality of gaps; and the first pinion is positioned between the first light source and the first light detector such that the first light bar has a first measurable transmissivity indicative of a measurable distance or angle of the rotatable shaft; and a second configuration comprising: a second light source that generates a second light bar; a second light detector to detect the second light bar from the second light source; a second pinion fixed on the rotatable shaft, wherein: the second pinion comprises a plurality of teeth and a plurality of gaps; and the second pinion is positioned between the second light source and the second light detector such that the second light bar has a second measurable transmissivity, wherein the second measurable transmissivity is different than the first measurable transmissivity at the measurable distance or angle of the rotatable shaft, and characterised by the first pinion and the second pinion having an angular sector of a disk shape, the angle of which is smaller than 180 degrees. a first configuration comprising: a first light source that generates a first light bar; a first light detector to detect the first light bar from the first light source; and a first pinion fixed on a rotatable shaft, wherein: the first pinion comprises a plurality of teeth and a plurality of gaps; and the first pinion is positioned between the first light source and the first light detector such that the first light bar has a first measurable transmissivity indicative of a measurable distance or angle of the rotatable shaft; and a first light source that generates a first light bar; a first light detector to detect the first light bar from the first light source; and a first pinion fixed on a rotatable shaft, wherein: the first pinion comprises a plurality of teeth and a plurality of gaps; and the first pinion is positioned between the first light source and the first light detector such that the first light bar has a first measurable transmissivity indicative of a measurable distance or angle of the rotatable shaft; and the first pinion comprises a plurality of teeth and a plurality of gaps; and the first pinion is positioned between the first light source and the first light detector such that the first light bar has a first measurable transmissivity indicative of a measurable distance or angle of the rotatable shaft; and a second configuration comprising: a second light source that generates a second light bar; a second light detector to detect the second light bar from the second light source; a second pinion fixed on the rotatable shaft, wherein: the second pinion comprises a plurality of teeth and a plurality of gaps; and the second pinion is positioned between the second light source and the second light detector such that the second light bar has a second measurable transmissivity, wherein the second measurable transmissivity is different than the first measurable transmissivity at the measurable distance or angle of the rotatable shaft, and characterised by the first pinion and the second pinion having an angular sector of a disk shape, the angle of which is smaller than 180 degrees. a second light source that generates a second light bar; a second light detector to detect the second light bar from the second light source; a second pinion fixed on the rotatable shaft, wherein: the second pinion comprises a plurality of teeth and a plurality of gaps; and the second pinion is positioned between the second light source and the second light detector such that the second light bar has a second measurable transmissivity, wherein the second measurable transmissivity is different than the first measurable transmissivity at the measurable distance or angle of the rotatable shaft, and characterised by the first pinion and the second pinion having an angular sector of a disk shape, the angle of which is smaller than 180 degrees. the second pinion comprises a plurality of teeth and a plurality of gaps; and the second pinion is positioned between the second light source and the second light detector such that the second light bar has a second measurable transmissivity, wherein the second measurable transmissivity is different than the first measurable transmissivity at the measurable distance or angle of the rotatable shaft, and characterised by the first pinion and the second pinion having an angular sector of a disk shape, the angle of which is smaller than 180 degrees.