[Aavso-photometry] Landolt error bars

[Ben Davies]

I want to get the U and  B error numbers for some of Arlo Landolt's 
standard fields and am wondering if the color error magnitudes given in 
his paper 
<http://articles.adsabs.harvard.edu//full/1983AJ.....88..439L/0000444.000.html> 
are just quadrature sums of the individual UBV errors.

If they are, and I want to back out the U and B errors, do I need to 
first convert them to flux-like values (ie not logarithmic), do the 
subtraction and then reconvert to magnitudes?

Also, in the paper, I notice that in numerous instances the (for 
example) reported (B-V) errors are smaller than the V errors.  How can 
that be?

Can anyone get me pointed me in the right direction here?

Ben Davies