Database error estimates

[Andrew Bennett <andrew.bennett@ns.sympatico.ca>]

I have downloaded and plotted error estimates
for some selected areas.

I don't understand the results!

For example, selecting MV in 11.9 to 12.1 I find a
range of standard deviations in the Database from
0.012 to 0.091 mags with clusters around 0.020,
0.040 and up, implying a wide range of
exposure times. Not true, I think?

The case that I can check, because I have the raw
data is Day 2452605: files HV/IRA2604797-863.
Specifically for a star of MV 12.0 near the centre of
HVRA2604797 I estimate a standard deviation of
0.061 mags for my least squares PSF fitting method
and around 0.064 to 0.067 mags for aperture methods,
depending on the size of the aperture.

The standard deviations in the Database are 0.019
to 0.022 mags for MV 11.9 to 12.1 in this image.

My estimate agrees with the Database values for data
on Day 2452301 (i.e. before the start of "Engineering" 
data) but not for any of the more recent data. Did
we have it right once and then "improve" the system?

I used:
Background s.d. 28.56 digits excluding sky background
Sky background 1886.3 digits
MV 12.0 equals 3321 digits total, 175.8 digits peak pixel

Andrew Bennett, Avondale Vineyard, NS, Canada