
What's been added in RPN55
Selling for the same price ($395) as the HP45 two years earlier, the HP55 offered more registers, more conversions, and programmability. In addition, it featured the timer already implemented in the HP45, but not made officially available to the user due to its pure accuracy and stability. The HP55 solved this by adding a quartzcontrolled oscillator.
RPN55 SD enhances the HP55 in many ways:
MEMORY 
HP55 
RPN55 
Register Arithmetic 
For STO operations on primary registers only

For both STO and RCL operations on all 20 registers, including the doubleregister ∑+ (R.1 and R.3) working with stack registers X and Y. 
Volatility 
Program and all registers lost on poweroff 
Program and all registers preserved ("continuous memory") 



TIMER 


Range 
100 hours 
12, 24, 100 hours 
CLx key 
Resets timer to 0 
100 hr: Resets timer to 0
12/24 hr: Sets timer to actual time 



FUNCTIONS 

r 
Not available 
Correlation coefficient 
x̂ 
Not available 
xestimate for given y 
ENG 
Not available 
SCI mode with exponent fixed to multiples of 3 
ABS 
Not available 
Make X value positive 
INT 
Not available 
Integer part of X 
FRC 
Not available 
Remove integer part of X 
RND 
Not available 
Round X to displayed value 
RAND 
Not available 
Create fractional or integer random number, as defined in Settings 
P≷S 
Not available 
Swap primary and secondary registers 



FUNCTIONS (with setting Replace Unit Conversions set to ON) 
sinh, sinh^{1} 
Not available 
Hyperbolic sine and inverse 
cosh, cosh^{1} 
Not available 
Hyperbolic cosine and inverse 
tanh, tanh^{1} 
Not available 
Hyperbolic tangent and inverse 
LOGy 
Not available 
Base y logarithm of x 
LN x! 
Not available 
Logarithm of factorial of x 
∆% 
Not available 
Percent difference from y to x 
%∑ 
Not available 
x as percentage of register ∑x 
PUSH 
Not available 
Saves the entire stack on a 4level stack 
POP 
Not available 
Replaces the stack with the last PUSHed values (0 if none) 
UNITS 
Not available 
Temporarily reveals the unit conversions until one of them has been executed.
This also works as part of a program. 
PSE 
Not available 
Pauses program execution for one second. 



PROGRAMMING 


Capabilities 
49 steps Editing by replacing steps 
99 steps
Insert and delete steps with automatic address correction 
Clear Program 
Not available 
Yes, with user confirmation 
Clear Program Range 
Not available 
Clear any block of steps with automatic address correction 
Delete f or g key 
Cumbersome 
Yes, by entering f or g again 



USER INTERFACE 


Prefix keys 
Active if pressed 
Active if pressed. Deactivated if pressed again. Indicators show state. 
Register view 
Not available 
All registers shown on single screen including formatted display.
Run/Stop and singlestep program without leaving register view.
Store and recall split times by tapping split number. 
Decimal Point, Thousands separator 
Fixed to decimal point (DP).
Thousands separator not available 
Userselectable, DP or comma.
Thousands separator optional 
Angular mode indicator 
Not available 
When not DEG, mode is shown in the topleft corner of the display. 
Command display 
Not available 
In program mode or while singlestepping, current command is shown as text below display 
Current step number display 
Not available 
Current program step number is optionally shown below display 
Program memory fill status 
Not available 
Red progress bar shows amount of program memory filled 
Low battery 
Lights all decimal points 
Lights all decimal points in vintage mode.
Lights a small red indicator in extended mode.
(When iPhone charge < 10%.) 
Switching to timer mode with x = 43.170992:
1. Vintage mode (100hr only)
2. Extended mode 100hr:
3. Extended mode 24hr:
4. Extended mode 12hr:




Importing Numeric Data 







You can preset RPN55's registers with data created externally without having to type them in. 



Simply prepare the data in text format in any app that can handle text, like Notes, Mail and many others. 







The data format looks like this: 



Rn or R.n value (where n = 0…9) 







Example:
To set R1 = 4.5, R6 = 6.28E7, R.3 = 439, prepare your data like this: 



R1 4.5
R6 6.28e7
R.3 439




Select all of the text and paste. 







Notes:
Upper/lowercase is ignored.
One or more blanks or tabs may follow the register number.
M may be used in place of R.
R.n may also be written as R1n, e.g. R.3 is the same as R13.
The order of the registers is irrelevant.
Unlisted registers are left untouched.




Extra Functions 







r 



Calculates the correlation coefficient for a linear regression.
Note that the method shown on page 61 of the Owner's Handbook calculates coefficient of determination, which is the
square of r. 







ABS 



Sets x to the positive value of x. 







INT 



Sets the fractional part of x to 0. 







FRC 



Sets the integer part of x to 0. 







RND 



Rounds x to the value currently shown on the display. 







RAND 



• If the RAND setting is Off:
Creates a random number between 0 (incl.) and 1 (excl.).
• If the RAND setting is On:
x ≤ 0: creates an integer random number in the range 0…2^{32}–1.
x > 0: creates an integer random number less than x, but no larger than 2^{32}–1. 







P≷S 



Swaps registers R0…R9 with registers R.0…R.9. 







LN x! 



Calculates logarithm of factorial.
This function allows handling factorials of very large numbers, as may occur
in statistical computations. By using the logarithm of these factorials,
multiplication and division are reduced to addition and subtraction.
On return:
x = LN x!
y = mantissa of x!
z = exponent of x!
(assuming x! = y·10^{z})
z+1 = number of digits of x!
x may be any positive number up to
4.4673259 × 10^{97}.








∆% 



Calculates the percent difference between y and x. The stack doesn't drop.








%∑ 



Calculates the percentage x is of the value in the ∑x register (R.1) 







PUSH 



Copies all four registers of the stack to an internal stack of stacks. Four levels are available. 







POP 



Retrieves the latest PUSHed copy of the stack. The current x value is saved in LastX. The oldest copy of the stack is copied down on the internal stack.
NOTE that CL.R clears the stack of stacks, while CL R does not. You can use P≷S CL R P≷S to clear the
secondary registers without affecting the stack of stacks. 







UNITS 



Example:
Calculate the base 2 logarithm of 5 inches converted to millimeters.
2 ENTER 5
f UNITS
g in➞mm
f LOGy
Result: 6.99
This sequence also works as part of a program.








PSE 



Executes a onesecond pause. A green indicator lights up while the pause is active. 



Timer 







Operation 



When you switch to timer mode, the current value of x is taken as the starting time.
If the value is an invalid time, 0 will be shown. Invalid starting times are negative numbers, or times equal to or larger than 100 hours (or 24 hours),
or more than 59 minutes in the minutes field, or more than 59.9999 seconds in the seconds field.
When leaving timer mode, the actual mode switching doesn't occur until the timer has been stopped by R/S. 







R/S 



Press key to start and stop the timer. This also works in register view. 







CLx 



100hours mode: resets the time to zero.
12 and 24 hours: sets the time to the current real time. 







EEX 



Shows or hides the hundredths digits. 







Split Times 



Pressing any digit key 0…9 while the timer is running stores the current time in the corresponding register.
Pressing any digit key 0…9 with the timer stopped retrieves the stored time from the corresponding register.
In register view, you can achieve the same by pressing any split time.
Nonzero values are highlighted in extended mode.
Split times are still available after leaving timer mode.








RAND 



• If the RAND setting is Off:
Creates a random number between 0 (incl.) and 1 (excl.).
• If the RAND setting is On:
x ≤ 0: creates an integer random number in the range 0…2^32–1.
x > 0: creates an integer random number less than x, but no larger than 2^32–1. 







P≷S 



Swaps registers R0…R9 with registers R.0…R.9. 
