Question about default value of `reltol`

[navidcy]

I have a question. Why is the default value of reltol often picked as sqrt(eps) and not e.g. eps? Is there a particular reason?

IterativeSolvers.jl/src/cg.jl

Line 122 in 40d9e9d

reltol::Real = sqrt(eps(real(eltype(b)))),

cc @elise-palethorpe