This specification specifies shape, size, spacing, and shading of letters and numerals to be used aboard ship. Characters are of Five Types: Type 1 -Plain letters and numerals (16 units). Type 2 -Block letters and numerals (12 units). Type 3 -Type 2 characters with shading (shading -1 unit). Type 4 -Block letters (10 units) and numerals (12 units). 1.2.5 Type 5 -Type 4 characters with shading (shading -1 unit). This specification does not give location or size of various shipboard markings incorporating letters and numerals.