Why does the Dry Air Gas Constant vary?

[Robert James Liguori]

I'm confused on why the dry air gas constant varies:

• Dry Air Gas Constant of 286.9 from The Engineering Toolbox
• Dry Air Gas Constant of 287.22 from https://www.physicsforums.com/ttp://www.peacesoftware.de/einigewerte/luft_e.html
• Dry Air Gas Constant of 287.05 from Brisbane Hot Air Ballooning
• Dry Air Gas Constant of 287.058 from Wikipedia

Can someone please explain why it differs and how it is constructed. Thanks, Robert

Reference:
[link to personal website removed]

 

[lychette]

to within 3 significant figures these are all the same !
It would be worth checking how each source obtained the value, especially the date when the values were measured.
Methods vary and improve over the years

 

[Robert James Liguori]

I am not a physicist... so you are implying that the differences in the values is insignificant? To me, it should be exact... or a means should be in place to get the exact value at each given location of sampling... if this was indeed possible, which it may not be. Please advise.

 

[Robert James Liguori]

universal gas constant = 8314.32 (in 1976 Standard Atmosphere)
molecular weight of dry air = 28.964

8.3143 / 28.964 = 0.28705634580859 (e.g., 287.056)

 

[Robert James Liguori]

I figured it out... thanks for your help.

[link to personal website removed]

 

[Chestermiller]

Can you measure the length of your kitchen table exactly? Why not? Are you going to let that keep you from buying a tablecloth?

Even if the value of the gas constant is not exact, does that bring your calculations to a screeching halt (until you find the exact value, which doesn't exist)? Isn't 3 significant figures accurate enough for you?

 

[DrClaude]

On these words of wisdom, the OP's question has been answered. Thread closed.