I have a detailed post with a diagram showing dosages on the syringe here for ya!
As long as you know your own mixing ratio – if you mixed your own hCG and you mixed 5mls of liquid into 1 vial of 5,000iu hCG, then in this case to take 125iu of hCG you’d go to the 12 (technically the 12.5) on your syringe – there may or may not be a hashmark for this on your syringe – but if you see the 10 or .10, that’s 100iu’s, then 12 or .12 would be 120ius, then you can just guesstimate a smidge above that for 125ius. But just go to the blogpost because seeing it in photos is much easier to understand I think!