What pen does the International Space Station use?

Under the condition of weightlessness in space, pens, ballpoint pens and other pens that use the principle of gravity cannot be used.

Pencils are the most convenient and cheapest on the International Space Station.

There is a joke that because pens and ballpoint pens can't be used in weightlessness in space, the United States has spent a lot of money to develop a pen that can be used normally in weightlessness and underwater. It showed off the astronauts of the former Soviet Union at an international space conference and asked, "Do you have such an advanced pen?" The astronauts of the former Soviet Union took a look and said disdainfully, "We only use pencils, which can be used in space and underwater." Americans are tongue-tied and speechless. When I got back, I said to the researcher in annoyance, "Why didn't we think of using pencils? Do you have to spend huge sums of money to develop new pens? "