An extension to a previously published work, this paper defines a new "diamond" orientation for the cubical-cavity benchmark problem in natural convection, and it presents new measurements on this as well as on a previously-treated orientation. Thus, measured were the average Nusselt number for an air-filled cubical cavity with two opposing isothermal faces and the remaining four sides having a linear temperature rise from the cold-face temperature to the hot-face temperature. The 95% confidence-limit uncertainties for Nusselt numbers (Nu) are around 1.2% for Rayleigh numbers, Ra, ranging from 10(4) to 3 x 10(8), and also for the "heating-from-the-side" orientation at Ra = 3 x 10(8). Thus the results are considered suitable for the testing of computational codes. (C) 2003 Elsevier Ltd. All rights reserved.