Yeah, because that wouldn't be a waste of my time at all. I think I'll pass. Have fun with your thread.
Sorry to say, you waisted your time when you suggested a calculation that would see air pressure fall to a level that is not possible. You could have chosen to put what I was trying to say into context or ask for clarification if you really wanted to be helpful; instead of trying to teach me how to calculate a percentage which was irrelevant to the query.
Nope, you'd rather argue, adamantly state I'm wrong and then offer no evidence to the contrary.
Your departure will not be missed...cheers.
The percentage change doesn't matter and I don't care what it is. I'm after the percentage change in air density or the percentage change that an object is affected by when passing through that air density. It's the point of the whole thread, you could have chosen to look at it a different way, despite how you understood my description..
I mentioned this earlier, but it may have been missed....
It seems to me that what you're looking for is a way to calculate the difference between a "normal" day at your course, and the conditions of any other day either at that course or another course that you may have traveled to.
The best way I can think to do that is by calculating the density altitude in the same manner that pilots do in determining operating performance for their aircraft. If the density altitude on any given day is significantly lower than whatever your baseline day is, you'll see a reduction in distance. If it's higher, you'll see an increase in what you're used to. The RELATIVE DENSITY is what you're looking for, but not as calculated, because that's calculated from sea level standard conditions of 15* C and 29.92 inches of mercury for temp and pressure. So you'll want to start by calculating the density altitude for your "normal" day at your location, then run it again for the current day. That will allow you to see the difference in the actual air density for both and you can calculate the relative difference between the two. Should give you a good point of departure for the day as to how those factors will affect your ball flight.
As a pilot, do you know of any calculations for change in drag coefficient with temperature and altitude? We are assuming that the effect of ball flight distance is directly proportional to the air density. But are there other factors that change? Does drag change with humidity and temperature? Pilot training may help us here.
I haven't found anything decent with web searches. The problem with searching the web is you get a lot of anecdotal information. All my text books deal with fluid flow of liquids mostly (Chem E).
These guys are smart.
But do they golf?
I found this calculator for the properties of air. Quick calculation between 760 and 745 mmHg shows a very small change in viscosity <0.1%.
So it looks like drag is directly proportional to density as well and the viscosity of air doesn't change that much. So we are back to only a 2% change in distance with a change from 760 to 745 mmHg barometric pressure.