Math is hard - help me with reconstitution please — anyone have experience?

Taking the question as asked, rather than the general version of it. Concentration choice is a precision decision, not a preference. Reconstitute high and every dose is a tiny volume where one unit of syringe error is a large fraction of the dose. Reconstitute low and you get more graduations per dose, so the same hand tremor costs proportionally less. Against that, more diluent means more benzyl alcohol and a shorter comfortable in-use window.

KevinCompounds said:

Concentration choice is a precision decision, not a preference.

That is correct as far as it goes, and here is where it stops going. The arithmetic is right and one caveat matters: a U-40 syringe changes the markings, not the volumes. If someone hands you U-40 and you read it as U-100 you will be 2.5 times out, and that error has a direction — it is always an overdose.

MariaRD said:

Two of us with identical vials and identical diluent arrived at different unit counts, which means one of us has a conceptual error rather than a…

This matches mine closely enough to be worth saying so. Dead space is the answer to the missing dose. A fixed-needle insulin syringe holds a few microlitres in the hub and needle after the plunger bottoms out, and on small draws that is a measurable percentage of every dose. Across ten draws it adds up to most of an eleventh, which is exactly the "nine draws from a ten-dose vial" complaint. Luer-lock syringes are worse; low-dead-space fixed-needle designs are better.

From the other side of the consultation, briefly.

Ongoing cost tracking for dosing arithmetic — transparency for the community:

Monthly medication cost: $152
Supplies (syringes, BAC water, alcohol swabs): ~$10/month
Janoshik testing: ~$12/month (amortized quarterly)
Lab work: ~$52/month (amortized quarterly)
Total: ~$232/month

Compare to brand Wegovy at $1292/month without insurance. Compounded is roughly 85% cheaper for what I have found to be clinically equivalent medication.