HP35s RPN Series # 3 [ENTER]

[Thomas Klemm]

(02-18-2015 08:24 PM)MarkHaysHarris777 Wrote:  1) other programmable calculators of the era (Wang 700, others) had register manipulators, but no [ENTER] key (certainly nothing like the HP RPN [ENTER])

Using the Wang 700 Programmable Calculator Simulator I have the impression that the [↑] key pretty much does what the [ENTER↑] key does: copy the number from the x register to the y register. I assume that's similar to how the 3-level stack of the HP-9100 worked:

Quote:Keying numbers into the stack did not cause the automatic stack lift that occurred on later calculators. For example, to calculate sqrt(25)+5, the user would press 2 5 [sqrt] [Enter] 5 +. The Enter wouldn't be needed on later RPN calculators. (Since calculator displayed the entire stack, the user always knew exactly where each number was and whether it needed to be copied up with Enter.)

When later calculators used a one line display, leaving results in an invisible stack register would have been a nuisance so RPN was altered. This later form of RPN popped the result down to the only visible register and then automatically pushed it back into Y when the user continued to enter data. When later HP models again used larger displays, the stack lift behavior was altered again.

Stack manipulation keys included an enter key (labeled only with an upward arrow), a drop key (labeled with a downward arrow) as well as ROLL keys for both directions and an X and Y exchange key. (X<->Y.)

With the one line display of the HP-35 the result of a calculation (i.e. what was the accumulator in register y) had to be displayed. But then this result shouldn't be overwritten with the next entry. Thus the number in display is moved to register y when a new number is entered. This is fine except immediately after the [ENTER↑] key. In this case what we call now stack-lift is disabled.

The HP-engineers came up with a clever solution for this problem.

Quote:2) the [ENTER] key is not necessary using consistent entry methods [+] with other register manipulators

Sooner or later you want to duplicate a number. You may call it what ever you like: [↑], [ENTER↑] or [DUP]. But the [+] key doesn't help here.

Cheers
Thomas