比例图 meaning in Chinese

proportion chart
scale map

" i do ; that is about the distance that separates your chamber from mine ; only , unfortunately , i did not curve aright ; for want of the necessary geometrical instruments to calculate my scale of proportion , instead of taking an ellipsis of forty feet , i made it fifty
“不错，那差不多就是你我两个房间之间的距离。可惜我没有把转弯弄对，我因为缺少必要的几何量具来计算我的比例图，本来只要挖一条四十尺长的弧线就行了，我却挖了五十尺。