There are different ways of mixing. I sometimes use a syringe for single flavours, or a 5ml cylinder for blends, but other times I will mix in drops. A drop is very approx 0.05ml, but it’s not really relevant even to know that, if you are familiar with the concentrate and know how much works in the blend.
I also mix up a big batch of unflavoured base mix. Then make 50ml bottles with flavour. I do t measure the base mix, just top up the bottle after measuring the flavour in. Because I never use more than about 5% flavour, it doesn’t knock the ratio or strength out by any noticeable amount, and is so much less hassle.
I’m sure many others will frown on these methods, but they work for me.