Slartibartfast has just finished designing the fjords of Norway. He begins work on the volcanoes of Hawaii when he soon realizes that his work isn't matching up with his blueprints.
Finally the answer hits him; his once faithful meter-long aluminum ruler that served him so well in the -10°C temperature of the fjords, after entering the 40°C tropical islands of Hawaii has expanded, and become 1.0012 meters long.
This may not sound like a lot, but when you are designing a coastline, 1.2mm per meter turns into kilometers worth of difference. And when he is working in the deeper, hotter parts of the volcanoes, this expansion of the aluminum ruler is only going to get worse.
What material can our worldbuilder design a measuring stick out of so it will stay as close to one meter as possible, regardless of what temperature he is working in? What sort of tolerance will the measuring stick have?