Input 755 has three ordinary permission digits. ChmodCalc adds explicit special digit 0 and displays 0755. This example chooses directory context, so each x is described as search or traversal rather than program execution.
0 · 7 · 5 · 5
Special digit 0 sets none of setuid, setgid, or sticky. Owner digit 7 is 4 + 2 + 1 = rwx. Group digit 5 is 4 + 1 = r-x. Others digit 5 is also r-x. Concatenating the three ordinary triplets gives rwxr-xr-x.
Directory meaning: owner rwx, everyone else r-x
For the directory mode bits, the owner has listing, entry modification, and traversal bits. Group and others have read and traversal bits but not directory write. Actual pathname access still depends on every parent directory, ownership class, ACLs, and system policy.
0755 is a decoded example, not a default
This page explains what the bits request. It does not decide whether a directory should be public, writable, executable, deployed, or recursively changed. A real GNU chmod invocation can also interact with existing directory setuid/setgid bits and other environment rules.