An Ordnance Survey cut mark in the UK. The term bench mark, or benchmark, originates from the chiseled horizontal marks that surveyors made in stone structures, into which an angle-iron could be placed to form a bench for a leveling rod, thus ensuring that a leveling rod could be accurately repositioned in the same place in the future.
9 Causes of Leaky Windows. One of the main reasons to ensure your windows are watertight is to keep moisture out of the walls. Once inside your walls, moisture can cause rot, mold and pest problems. Keeping water at bay would be easier, of course, if our homes had no openings for doors and windows.
More than likely this may just be mildew from condensation and air infiltration. Mold and mildew develops on your window sills because the window frames are not thermally broken.This allows condensation to form on the inside of the frames during cold days and winter months. 1  The formation of condensation could be an indicator that your humidity level inside the home is too high.