The distance calculator measures the straight line flight distance ("as the crow flies") between points.

距离计算器措施直线飞行距离（ “为乌鸦苍蝇” ）之间的分。

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Also for pre-planning, the free Flight Calculator Windows app estimates carbon emissions for flights around the world and gives an option to immediately purchase offsets that fund a range of verified projects from Carbon Footprint Ltd.

BBC: How big is your carbon footprint?