  A finite size effect in the probing of the harmonic measure in simulation of
diffusion-limited aggregation (DLA) growth is investigated. We introduce a
variable size of probe particles, to estimate harmonic measure and extract the
fractal dimension of DLA clusters taking two limits, of vanishingly small probe
particle size and of infinitely large size of a DLA cluster. We generate 1000
DLA clusters consisting of 50 million particles each, using an off-lattice
killing-free algorithm developed in the early work. The introduced method leads
to unprecedented accuracy in the estimation of the fractal dimension. We
discuss the variation of the probability distribution function with the size of
probing particles.
