UK scientists working towards a redefinition of the kilogram

Scientists at the National Physical Laboratory (NPL) have released new
research results that could affect how we measure a kilogram - the
last SI unit based on a manufactured object.

http://theanalystmagazine.com/pr/401091.htm

On a sunny day (Fri, 02 Nov 2007 02:21:55 -0700) it happened
wrote in
om:

Scientists at the National Physical Laboratory (NPL) have released new
research results that could affect how we measure a kilogram - the
last SI unit based on a manufactured object.

http://theanalystmagazine.com/pr/401091.htm

It says:
The value of Planck's constant calculated from the latest NPL results is 6.62607095(44) x 1034 J s [66 x 109].
This value of Planck's constant differs by 308 nW/W from the result published by NIST in 2007 of 6.62606891(24) x 1034 J s.

mmm, changes over time? measurement errors? systematic errors?

It says:
The value of Planck's constant calculated from the latest NPL results is 6.62607095(44) x 1034 J s [66 x 109].
This value of Planck's constant differs by 308 nW/W from the result published by NIST in 2007 of 6.62606891(24) x 1034 J s.

mmm, changes over time? measurement errors? systematic errors?

h is a constant it means that dh/dt = 0, an universal constant can't
change over times (if it is correctly defined)

Probably an instrumental error or a systematic one is the better
explanation.

Are we (they) sure that only last two digits are affected by
statistical error in both cases?

[P.S.: Sorry for my bad english]

Q