Answering the narrow version, because the broad one does not have a single answer. 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.

anders_CPH said:

Concentration choice is a precision decision, not a preference.

No disagreement with anders_CPH. One condition attached. 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.

I would rather be corrected than agreed with, if it comes to it.

paul_denver 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…

Same position here, arrived at the long way round. 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.

Adding the clinical framing, because it changes how the question reads.

Just received my dosing arithmetic order — packaging review:

• Outer box: plain brown, no medication identifiers (discreet) ✅
• Inner insulation: Styrofoam with 3 gel ice packs ✅
• Temperature: vials were cold to touch on arrival ✅
• Labeling: lot number, BUD, compound name, concentration ✅
• Included: COA, reconstitution instructions, dosing card ✅

This is what professional compounding pharmacy shipping looks like. If your order arrives without these basics, reconsider your vendor.