Burnt, wood undergoes both mass loss and charcoal fragmentation. Consequently, the distribution of the charcoal-pith distances does not indicate unburnt wood diameter. Therefore, an Analysis Diameter model (ADmodel) was developed, based on the fact that a trunk is biologically considered to be a stack of cones.These cones are hollow and their thickness corresponds to the amplitude of the diameter classes. It is based on a
calculation table that provides the respective distribution of these cones in terms of volume. The ADmodel breaks down unburnt wood diameter into an expected distribution of charcoal-pith distances. In return, the ADmodel is a helpful tool to interpret the distribution of charcoal-pith distances from a charcoal assemblage as unburnt wood diameter (UWD). However, this model does not reconstruct the initially quantity of burnt wood.

Reference
Dufraisse A., S. Coubray, O. Girardclos, N. Nocus, M. Lemoine, J.-L. Dupouey, D. Marguerie (2018). Anthraco-typology as a key approach to past firewood exploitation and woodland management reconstructions. Dendrological reference dataset modelling with dendro-anthracological tools. Quaternary International, Vol. 463, Part B : 232-249.

For more details, see
Dufraisse A. (2006). Charcoal anatomy potential, wood diameter and radial growth. A. Dufraisse (ed.), Charcoal analysis : new analytical tools and methods for archaeology. Papers from the table-ronde held in Basel (October 2004). Oxford : Archaeopress, p. 47-61 (BAR International Series).