M: I'd be happy to help you. What would you like to know？
W: First of all, how was the standard weight used？
M: Well, the people in our department use it to check the scales all over the country. The department of weights and measures, we are a government agency. It's our responsibility to see that all the scales measure a kilogram accurately so this is the way we use to adjust the scales.
W: How did you check the scales before？
M: We have an old standard weight that we used to use. It had to be replaced because it was imprecise. Yon see it was made of poor quality metal that was too porous. It absorbed too much moisture.
W:Oh. So when the weather was humid it weighed more and when it was dry it weighed less.
M: Exactly. And that variation can affect the standards of the whole country. So our department had the new weight make out of higher quality metal.
W: How much did it cost？
M: About 45 thousand dollars.
W: 45,000 dollars？ For one kilogram weight？ That's more expensive than gold. Is it really worth that much？
M: I'm sure it is. Industries depend on our government agency to monitor the accuracy of scales so that when they buy and sell their products there is one standard. Think of the drug industry, for example, those companies rely on high accuracy scales to manufacture and package medicine.
What is the conversation mainly about？

A. How to care for precious metals.
B. A standard unit for measuring weight.
C. The value of precious metals.
D. Using the metric system.