Not all units of insulin are created alike. We switched back to the pump over Labor Day weekend from insulin shots.* When we switched her from 28 units of Lantus, which acts like the pump's basal delivery, you would think that by simply giving her 28 units of Novolog equally over 24 hours should accomplish the same thing. This turned out not to be the case. She actually needed less insulin over a 24-hour period. So 1 unit of Novolog doesn't equal 1 unit of Lantus. I suspect that's probably true for Humalog, NPH or Regular. 1 doesn't always equal 1. Good to know for the next switch you do.
*I think it was a pretty good idea to do a switch in Cassie's insulin regimen over a long weekend so we have more time to work out the kinks.