densitometer
(1)光密度计
(2)显象密度计
(3)黑度计

• ruby ranging laser
• ruby rod
• rudimentary compound microscope
• ruff
• ruggedness
• rule
• ruleability
• ruled area
• rule depth ga[u]ge
• ruled grating
• ruled surface
• rule-of-thumb relation
• ruler
• ruling
• ruling engine
• ruling grating
• ruling span
• Rumford's photometer
• run
• run-length coding
• runner
• runner cut
• running fit
• running wave
• rupture