The IP rating, or protection level, that you need will vary from job to job. What is most important is knowing the context you will be using your gage in and then deciding the degree to which you require protection, and from what specifically you want to protect your gage. Some precision measurement contexts will involve high pressure water tools and you will want a higher number IP rating to account for this. However, others might involve no risk of water being nearby, but be in a setting with a great deal of construction that will lead to accumulated dust. You will need to focus on a higher first digit in your IP rating for this purpose. Finally, there is a certain amount of protection that you can strive for concerning potential risks that may or may not happen. For example, there might not be water directly in the vicinity, but there might be a sink nearby that runs the risk of overflowing with regular use. Alternatively, the area where your gage will be used might not be scheduled for regular cleanings, or not be cleaned until the end of the project, so you will want to account for potential dust build up. There are many moving pieces to each precision measurement context, and you will want to know the specific risks you have to determine the best IP rating.