Hi Claire, welcome to the forum 🙂 I agree with Sally - it will vary from person to person how much levels will be reduced by one unit of insulin, because it will depend to a large extent on how sensitive they are to insulin in the first place - some people need only very small amounts of insulin with their meals, for example, so an extra unit might bring their levels down more than 3 mmol/l. The principle is correct though 🙂 The amount extra that you use for a 'correction' should therefore be agreed with his DSN, and it's worth doing a couple of extra tests if possible just to keep an eye on how well it works 🙂