I think you're making it more difficult than it needs to be due to the amount of BAC water you are adding. Your method is requiring decimals and partial units to be used, when that's unnecessary.
**place 2.1 ml of bac water in a sterile empty vial
**add the .5 ml of hcg from the ovitrelle pen
**you now have 2.6 ml of hcg, and this 2.6 ml contains all 6500 iu of hcg from the pen
**this 2.6 ml mix you just prepared will yield exactly 26 injections at 250iu each, assuming/providing that you draw 10 units (on your insulin syringe) for each injection
**basically, each unit on a slin pin will provide 25iu of hcg, so it will be very easy to measure out 250iu, 300, 500, etc.
Trust me,
@Fckit,
@greenddog1, myself and others already spent too much time figuring this out! Haha
And thanks to both of those guys and others for the help factoring the above.