If the object we select for the Earth is 10 inches across, what is the scale of our model (in inches/km)? The Earth is 12,756 km across.?
I suggest that we convert both of the distances to meters. d1 = 10 in * 2.54 cm/in * 1 m/100 cm = 0.284 meter d2 = 12,756 * 1000 = 127,560,000 Scale = 0.284 ÷ 127,560,000 The scale is approximately 1 to 2.2 * 10^-8
Seriously?!? Did you sleep through elementary school math? 10in. = 12,756km 10in/10 = 12,756km/10 1in = 1,275.6km
this is why people tend to avoid mixing US standard and metric. 10 inches is 0.254 m (very close), so we can say that 0.254 m in the model is 12.7 x10^6 m of real world, which is about 1 : 50 million. 0.01 m is 500,000 m or 500 km. 0.25m (25 cm or 10 inches) is 12,500 km. close enough for government work, I would say.
10 in / 12,756 km = 0.0007839 in/km