optical indicator
(1)光学指示器
(2)光学示功计

• spacing hole
• spacing piece
• spacing ring
• spaci tor
• spaghetti
• span
• spanner
• spar
• spare parts
• spark
• spark light source
• spark plug
• spark spectrum
• spar-over
• Sparrow's criterion
• spatial acuity
• spatial angle
• spatial brightness
• spatial carrier
• spatial character
• spatial coherence
• spatial coherence function
• spatial degeneracy effect
• spatial distribution
• spatial domain