01 / Input example
Simple geometric example: overall width 1,200 mm, with a 50 mm frame on each side. Under these assumptions, clear width is 1,200 − 50 − 50 = 1,100 mm.
02 / Check assumptions
Check whether overall means the outside of the frame or the rough masonry opening. Door leaves, fittings and finishes can reduce actual usable width.
03 / Scope of use
Record units and dimension type before consulting a ruler. The brief describes three cycles of 522/429/388 mm; the chosen ruler must suit the object being measured.
04 / Keep in mind
An auspicious interval is feng shui information, not a substitute for accessibility, egress, ventilation or other technical checks.
Tool introductions do not validate algorithms or certify regulatory compliance. Guides are practical examples; design and construction decisions require checks against project documents, applicable rules and qualified professional judgement.