You can edit the Size field to include more valve sizes via Vitals Desktop. Once it is updated in Vitals Desktop, you will have to do a FlashTransfer or Data Transfer between the TC-100/HC-100 and Vitals Desktop. After the FlashTransfer or Data Transfer the TC-100/HC-100 will have the updated Size field. 

See steps below on how to add a new valve size:

In the Customize Data Fields window make sure you select Valves from the dropdown. Then click/highlight the field name you want to update (Size). Then click Edit Choices. On the Edit Choices window, just add the new size to the list as shown. Should be one size per line as shown in the picture below. Click OK to save.

Perform a data transfer with the TC-100/HC-100 per the Vitals Manual.