We sometimes will suggest if you are using U40 strength PZI, that you switch from U40 syringes to U100 3/10cc syringes (for 30u or less) with half unit markings in order to more accurately measure insulin doses (between the bold numbers, there will be two lines of marks, four to the left in between four on the right.  The lines on one side are for whole units, the lines on the other are the half unit markings).  With U100 syringes, a unit of U40 insulin can be broken down into five 0.2u increments (5 x 0.2u = 1.0u). This makes smaller changes to dosing much easier and far more accurate, as you are not eyeballing your measurements and hoping like heck to get the amount right. 

Below is the conversion chart used to measure draws on the syringe, and an adjusted starting scale for using U40 PZI with U100 syringes.

Please be aware that there are several sizes of U100 needles, each holds different amounts of fluid - 3/10cc/ml, 1/2cc/ml and 1cc/ml.  The 3/10cc and the 1/2cc both have draw lines on the barrel that equal one unit, while each of the draw lines on the 1cc syringe equals two units.  It is important NOT to buy the 1cc syringes, as the 2u draw lines can make it very easy to overdose!

Buy only 3/10cc syringes with half unit markings!

As far as the conversion goes, what you are dealing with is a "volume" issue when using U100 syringes, compared to U40 syringes. If you hold a U100 syringe beside a U40 syringe, you will notice the U40 syringe is a lot fatter than the U100 syringe. If you were to take 1.0u and fill each syringe, you would see that it looks like there is a lot more insulin in the U100 syringe than in the U40 syringe B this is because U100 insulin is pure insulin, while U40 is diluted with water - i.e., U40 is 40% insulin and 60% water, so the water adds more volume to the insulin, making it look like more.  A unit of U100 is one unit of insulin, and a unit of U40 is one unit of insulin with 60% more water added to it - both are still only one unit of insulin.

When drawing U40 insulin into a U100 syringe, there are two steps to preparing your dose. First, identifying the amount of the dose. Second, identifying the DRAW on the syringe. The conversion factor for volume is 2.5 B meaning that if you need 1.0u of U40 insulin, you need to DRAW to the 2.5 line on the U100 syringe. You will identify the amount of your insulin dose on the conversion chart, then move across the line on the chart to identify the amount of the DRAW on your syringe.

You will need to adjust the way you keep your off-forum test log, adding a column to record the DRAW on the syringe, as well as the dose amount. You want to post only the ACTUAL DOSE on your DCC test log B the DRAW amount is for your records only.

Once you make the switch, put the U40 needles away somewhere (in a completely different place). You don't want to be using a U40 syringe by mistake.