What are some possible sources of error in using the ruler/triple beam balance? me .

Slanting or not being straight in measurements 
... hopefully this will help 

Non metal is an element or substance that is not a metal metal is a solid material that is typically hard, shiny, malleable, fusible, and ductile, with good electrical and thermal conductivitymetalloid is an element (e.g., germanium or silicon) whose properties are intermediate between those of metals and solid nonmetals. they are electrical semiconductors.