The most common mistake in an at-home peptide log is carrying a memorized syringe mark across a change in reconstitution. Ten units on a 5 mg vial mixed with 2 mL is not ten units on the same vial mixed with 1 mL; it is half the dose.
Two formulas prevent that. Concentration equals vial strength in mg divided by diluent volume in mL. Volume equals dose in mg divided by concentration, and on a U-100 insulin syringe 1 mL is 100 units. So a 5 mg vial in 2 mL gives 2.5 mg/mL, and a 250 mcg dose is 0.1 mL, or 10 units.
A log entry is only useful months later if it records four things: the date and time actually administered rather than the one scheduled, the compound and dose with the unit written out, the concentration in effect at that moment, and the injection site. Site rotation only shows up in the record if you write it down.
I keep mine in Peptide Tracker & Calculator, which stores the vial record alongside each entry so old doses keep the concentration they were taken at. The reconstitution calculator is the part I open most often.