Typical C α distance in β -sheets. Typical Cα distances computed from the Ref set in parallel (left part) and anti-parallel β-sheets. Mean distances are indicated in Å with their standard deviations within parentheses. Separate statistics were computed for distances involving only residues in strand cores (italic) and distances involving residues at strand edges (bold). For the intra-strand distance (type i to i + 2), no distinction is made on the sheet orientation.