It's common for scientists to prefer a decimal point in their measurements because they are inherently limited precision, but "1 mm" leaves some ambiguity as to whether you meant 1.0 mm or 0.1 cm. It's a matter of significant digits, since leading zeros are ignored.
If you are interested in this kind of stuff this is called Macro photography and it can be very complicated or confusing when you start but it's very rewarding and after you get the basics it's not hard. For some truly mind blowing photos I suggest you check out Alison Pollack on Instagram she has placed in several world wide macro photo Competitions and she specializes in fungi.
Mycena subcyanocephala is a species of fungus,[1] which has its habitat in the tropical parts of Taiwan. It has been spotted eight times. Mycena subcyanocephala is one of the smallest mushrooms in the world, with buttons about 1 mm tall. The species belongs to the Mycenaceae family, with Mycena interrupta being its closest relative.