The figure for a proton's rest mass, 1.67262171 x 10^-27 kg, is an experimental result rather than a derived calculation. This value is expressed in scientific notation, which simplifies the representation of very small numbers. The discussion highlights the importance of understanding the context of this number, emphasizing that it is not merely a calculation but a precise measurement. The Penning Trap is mentioned as a method used in determining proton mass. Overall, the conversation clarifies the distinction between numerical representation and the actual mass of a proton.