Gun sights introduced early in the nineteenth century consisted of fixed front and rear sight points so adjusted that the line of sight across their tips was parallel to the bore of the gun.
十九世纪初的火炮瞄准具由炮身前后两个尖点构成，视线通过两尖点顶端就得出与火炮炮膛平行的瞄准线。
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The sight telescope was mounted in such a way that the line of sight could be offset from the axis of the bore of the gun to correct for range, drift, and relative motion of gun and target.