straightness of line of sight
瞄准线，平直度

• silver halide
• silver halide emulsion
• silver spot
• similarity
• similarity law
• similarity theorem
• simmering lamp
• simmer operation
• simple harmonic motion
• simple layer film
• simple lens
• simple magnifier
• simple microscope
• simple ocular
• simple periodic motion
• simple reflection goniometer
• simple (single) lenses
• simplex
• simplicity
• simplification
• simplified view
• Simulatan
• simulating test
• simulation
• simulator