I get where you're coming from when you're just getting started. The numbers threw me off back then too, and making sure they're handled correctly really counts. Begin with the core ideas. Weight gets measured in milligrams, a thousand of them adding up to a gram, and that gram size feels substantial with these substances. Micrograms show up less, since a thousand equal one milligram and that's an extremely tiny amount. Liquids go by volume instead, with milliliters matching cubic centimeters exactly.
Needles usually have markings in units, where a hundred equal one milliliter or cubic centimeter. They come in three typical capacities of a hundred, fifty, or thirty units. Most people use twenty-five to fifty units at a time. The smaller sizes help when dealing with tiny volumes because the lines sit farther apart, making them simpler to read accurately. Refillable pens work with one click per unit, so twenty-five clicks line up with twenty-five units. Keeping an eye on decimal points stays crucial, since mixing up twenty-five milligrams with point two five would cause real problems.
I still note the steps on paper and calculate them one by one. Hanging onto those notes comes in handy. It can look tricky at first but turns out easier than it seems and improves once you repeat it a few times. I pull out some needles and test things using water, reaching for a calculator if it helps. Questions never hurt. Sorting out the starting points matters a lot. Plenty of clips exist online and some people here post their mixing and dosing tables right after their messages. My time back in the sixties left me without the knack for making those myself.