I was watching a show on TV with some of my friends, where these guys were literally taking badly rusted cars - they were literally junk pots, and turning them into beautiful "vintage" automobiles that would go for several hundred dollars. We were chatting about a similar program on MTV I used to watch called "Pimp my ride" where cars fit for the junkyard were modified, cut, converted and painted into beautiful machines.
The guys I was hanging out with happen to be engineers and we ended up discussing the pro and cons of sand blasting rust off cars. I learnt that's not a very good idea as it can do more damage. Anyway, sandblasting is quite popular and that was what the guys in the show were doing. They removed the rust, patched the holes and scratches, painted them to what I thought was a really high standard. However, my engineer friend told me that the only way to confirm the smoothness of the surface is by using a 'surface roughness tester' also known as a profilometer. Yes, you learn new things everyday.
Apparently you can quantify the roughness of a surface by measuring the surface's profile. Most of these are big machines in the labs but I also found out that there are even hand held portable versions. For example, blast cleaned surfaces can be tested for the peak-to-valley height using a Portable Surface Roughness Tester Profilometer (yes, that's the official name of these machines). I did not get much of the technical stuff, but that's how the experts test the smoothness (or roughness) of metalworking or even a paint job.
So if you have a workshop and want to known as a professional today, your shop floor has to have one of these gadgets.