Chromatin DNA is packaged in the nucleus in basic structural units called nucleosomes, each consisting of a segment of DNA wound around eight histone proteins. Nucleosomes are evenly spaced along the DNA unless they are interrupted by other structural landmarks such as transcription factors. What determines the spacing and phasing distances of nucleosomes is unknown, but the answer seems to lie with a group of proteins called chromatin remodelers, which are known to assemble, slide, and dismantle the histone part of nucleosomes. Oberbeckmann et al. show that some chromatin remodelers also contain a ruler element. Using this built-in ruler, these remodelers sense and process information in the nucleosome environment and then adjust nucleosome sliding direction bias, thus determining the spacing and phasing of nucleosomes. Nat. Commun. 12 , 3232 (2021).