Yes, you have it right. Basically, if you are using 1 cc insulin needles, it will be the 25 mark on the syringe. That is .25cc That is 250iu so you will decrease or increase it to 225 or 275. That will be .22 or .27 on the needle. It will be two or three marks above or below the 25 mark. I hope this helps.
Using a 5000iu amble of HCG at does of 250iu or .25cc, you get 20 days. Does that make sense?
More Info...
Here is a link that might help understand IUs. http://www.onlineconversion.com/faq_02.htm
and here is a link on mixing and doses.
http://www.hcgsupplies.com/hcg-mixing-directions.html
Note: 1 ml = 1cc 1cc/ml per 1000IU of HCG (this maybe different for other drugs and vitamins)
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My JournalTotal losses using HCG 100lbs plus number on ticker.