Imagine you are in a lab, and you have before you a Wintel device displaying a recipe from a custom software program. The display would be on a typical low cost flatscreen display. In the recipe, you have component names, and the quantity of that component required. The component quantities add up to some total amount. Reading the recipe, you go to various shelves in the lab and pull jars of components towards a scale. Weighing each component, you place the required quantity into a new container. And, as you weigh each quantity, you reach for...a pen that you use to (a)select (click on) the component you added and (b) write the quantity you weighed out. Now, you are not using a surface sensitive display so you cannot write on the screen like some of the modern tablets and laptops allow. But, you can "write" on any surface, such as a lab counter, and somehow the pen recognizes the numbers and decimal points you gesture. On the screen, your gestures show up as handwritten numbers, then as if by magic, the numbers are converted to computer-readable numbers and placed into the text block where you are supposed to enter these weights. The numbers become actual digits that are recorded in the software creating a record of your quantities. You then click "save" and "submit" and that mixture is recorded for all posterity.

Are there such pens that can be used? Ones that are durable, droppable, cleanable, etc?

what program are you recording these numbers in. edit I see you said custom...

There are possible options but they will not be on any surface and will require a USB hook up. Like this