Hi, Ingrid.
This is a restatement of issue 69423 as requested. It is common in science to
show graphs with number of counts in the ordinate. When these counts reflect
statistical variation around a constant rate, the distribution is Poisson, and
is well approximated by a normal distribution with standard deviation given by
the square root of the ordinate value. 
This should be very straight-forward to code by copying the code used to produce
% error bars.  

While suplying error bars from a range (766) is a long-standing request which
would aloow the user to do this, 766 has been delayed for years presumeably for
technical reasons. Including one of the common error estimates is a useful
simplification of a common case, and should not suffer the 766 delays.