Just to reiterate the most important point
insulin activity is not "one size fits all"
If I need to lover my blood sugar from 180 mg/dl (10 mmol/dl) to 125 mg/dl (7mmol/dl) ... I would need to take 550 units of insulin.
that means that 10 units of insulin reduces my BG by 1 mg
Most diabetics with no insulin resistance will see a ratio of between 1unit = 15-18mg ...