Check your progress relative to your reference line frequently. And check for square frequently with a combination square.

刨的过程中要经常根据刚才画的参考线检查刨削的进度，并用组合直角尺检查是否方正。

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This combination is named the square of the "interval".

人们把这个组合称作“间隔”的平方。

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But the actual record, 4.17m square km in 2007, was the product of an unusual combination of sunny days, cloudless skies and warm currents flowing up from mid-latitudes.

真正的记录是2007年的417万平方公里，是连日晴朗无云和来自中纬度的暖流共同作用的结果，实属偶然。

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More experiments with the stuff in the brightest square (a combination of oxygen with the metals gallium and gadolinium) led to a surprising conclusion.

ECONOMIST: Combinatorial chemistry