The 12C is great for easily calculating a standard deviation on a list of numbers, using the standard deviation key and the statistics keys (sigma +).

But is it possible to get the geometric mean from the HP 12c or 12cp from the same accumulated statistics without rekeying them all or entering a separate program?

I doubt it.

It is possible to calculate the geometric mean, if you have the product of all the entered values. However, the 12C calculates and stores the summation of the entered values, not the product.

In theory, it should not be difficult to calculate geometric means and geometric deviations on the 12C. Instead of the sigma-plus key, you could substitute a simple programmed function that would first calculate the natural log, then enter the log-transformed value into the stats registers via sigma-plus.

When all of the log-transformed values had been entered, you could calculate the mean or s.d. of the log-tranformed values as usual. Then take the antilogs to get the geometric mean or geometric deviation.

The 12CP allows for 80 cash flow numbers that are accessible as an array of sorts. It would be simple to write a program to calculate the geometric mean/sd of them. You could also compute the arithmetic mean/sd of them without re-keying them in. Entering them as cash flows is just as easy as using Sigma+.