Although you may need to be trained to use observational equipment in science. You should be able to get the same observation using that equipment as someone else for an observation to be valid.
When measuring what has been observed, you have two methods. The one you use is the one that is practical and will produce meaning.
|Smoke cloud from fire|
in Denali National Park
Quantitative is when you measure an item precisely like how many lightyears a star is from the Earth or how many grams of a medication compared to the mass of an individual, plant or animal produces optimal results.
What you can't do is quantitatively measure how much water is on the Earth. What you can do is measure the percentage of salts in ocean water. I remember in college, learning that the percentage of salt in the ocean was the same as it was in a living cell. This was proposed as result of the ocean being the primordial soup in which all organisms originated.
Then a teacher pointed out no, the ocean was not consistently the same salinity all over the world. Some oceans had so much fresh water added that they had very low salinity like the North Sea which has about 1 percent salt. Some seas/oceans have so much evaporation and so little input of fresh water, they were very saline (or salty). The Pacific and Atlantic have roughly 3.5 percent. The Dead Sea has roughly 33 percent.
But that tidbit of fact I learned was true in that if you measure the composition of salt in ocean water all over the world, the types of salts are all the same whether it is in a river or ocean and reflect the elements available in the Earth's crust.
And that is an example of a qualitative description. A qualitative description describes an object or condition. Diabetes II is often called Diabetes mellitis for the sugar found in the urine. Yes, at one time, someone tasted the urine to detect the excess sugar. Having a high concentration of sugar in the blood is a quality. Having a blood sugar level between 70 and 120 mg per dl of blood is normal. Using mg per dl is an example of quantitative.