(11-24-2017 02:36 PM)PANAMATIK Wrote: (11-24-2017 12:14 PM)Dieter Wrote: BTW, comparing both machines, it is nice to see what a difference one year makes: The 1976 HP67 already uses 13-digit internal precision while the HP25 still has to rely on merely 10 digits for internal intermediate results. Consequently the infamous 3^{201} example has only 6 (!) correct digits (after rounding).

I don't think the HP-67 has higher internal precision than the HP-25, both represent a number as 10 digit mantissa and 3 digit exponent with sign. Perhaps the 15-digit HP-67 display suggests a higher precision. [...]

HP Journal, November 1976, pp. 16-17, has a sidebar titled

The New Accuracy: Making 2^3 = 8, included in the MoHPC document set, which mentions using extra digits for intermediate results. It doesn't say how many, and it does indicate that this extra internal precision was not used for all functions. It does mention using a 13-digit approximation of pi internally, for argument reduction.