On the drawing of a watch with a scale of 200:1, the diameter of a circular part is measured to be 3 cm. What is the actual diameter of the part in mm?
在比例尺200：1的手表图纸上，量得一个圆形零件的直径为3厘米，求该零件的实际直径是多少毫米？
<gadget id="calculator">200 / 1</gadget>
<output>200</output>

<gadget id="calculator">3 / 200</gadget>
<output>3/200 = around 0.015</output>

<gadget id="calculator">(3/200) * 10</gadget>
<output>3/20 = around 0.15</output>

<result>3/20 = around 0.15</result>