Yesterday, I discovered that, when I asked Siri for the temperature on my iPad, it would
always tell me the temperature in fahrenheit, even though I am in France, and my time zone is set as such. (There is no real country setting on iOS.) On my iPhone, however, I would get the temperature in centigrade, as expected. A friend suggested that this is because I had set C in the Weather app on the iPhone. As there is no Weather app on the iPad (I still don't know why), there's no place to make this change.
Fortunately, a commenter to the blog post I linked to above pointed out that there is, indeed, a way to set the temperature, but it is well hidden. Open Clock, tap on Edit, and you'll see two buttons at the bottom of the clock list, one for F and the other for C. It seems that the only reason this setting is here is because the clocks can show time and temperatures. But unless you live in a major city - one for which you can choose a clock - the temperatures here aren't much use.