HP-29C: 98 Program Steps, So, why not an even 100?

[rprosperi]

(08-31-2019 02:18 AM)bshoring Wrote:  Hi Bob,

I presume you are referring to the paragraph near the middle of page 49 (of the HP-38 Owner's Handbook), that begins with "The Nj key is designed..."

My take is that this is not necessarily in conflict with the diagram at the beginning of the manual. I have my HP-38C right next to me. The CFo and CFj functions do store the value of the original or subsequent cash flows in R0 through R.9. That would be amounts such as -100,000, 5,000, etc. But the Nj key allows the user to enter a number between 1 and 99 (to indicate the number of times such cash flow occurs. When you enter a value using CFo or CFj, the value of Nj is set by default to 1. But if you want to show, for example monthly cash flows in the same amount then you have the option to set Nj to 12 or any number as long as you don't go higher than 99.

So that tells me there is a small memory space set aside to accommodate the 21 Nj registers of 2 digits. I believe 2 digits can be stored in one byte, so if there are 21, then it seems to me they set aside 3 full (7 byte) registers to hold the 21 values.

My two cents...

I suspect you're exactly right Bob, nice catch! The diagram at the front of the manual labels these financial registers as N0 - N20, so a total of 21 registers which matches the allowed number of groups of cash flows (20) plus the initial investment, all labeled Nn.

So these cash flow 'counts' are stored in these dedicated 2-digit storage places, apparently part of the 32 available registers Tony described. Also, I've just now noticed that these N registers are shown smaller (narrower) than all the other registers in the graphic illustration.

I also checked the Quick Ref Guide, which also has a pictorial depiction of all the storage on the cover, but these cash flow counts are not shown or mentioned.

Thanks for your comments Bob, I always enjoy discussing and learning about these great old machines. Sadly, it appears you and I are about the only folks left that like and use a 38E/38C.