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Steve's RPN Curta Program

This program implements a tool for calculating time based on inputted speeds and distances.  It was designed to be used on TSD rallies.  The general design is based upon the abilities and interface of a Curta mechanical calculator. 

Environment

The program is written in the scripting language for Russell Webb's RPN calculator.  You need to hav the RPN calculator to use it.  Registered version of the software is relatively cheep.

Later in this document you will find instructions for installing the program in the calculator. 

What is an RPN calculator?

RPN stands for Reverse Polish Notation, I prefer the term postfix notation because I'm a dork.  With postfix notation the operators follow the numbers.  "2 + 2" becomes "2 2 +".  Postfix notation requires a stack structure, to use the Curta program you don't need to understand the stack but be aware that you can see it on the display of the calculator.

What you do need to know about using this program which is built into a RPN calculator is that you put input values into the calculator then do the operation on them.  If you want to input a speed (CAST), you type the number in then hit the CAST button.

What is a Curta?

A Curta is a mechanical calculator that looks like Buck Rogers' pepper grinder (if Buck Rogers had a pepper grinder).  The large dual accumulating registers make the curta a powerful tool for calculating times based on speed (actually a time to travel factor) and distance. 

At some larger rallies you can sometimes see a few people calculating the times with their Curtas.  It fun to watch someone who is good use one, they are able to calculate very quickly. 

If you want a demo of Curta usage ask me and I'll bring one to an event.  Of course, I usually bring one (or two) to most touring rallies just in case my palm goes tits up. 

See the Curta Calculator Website for most everything you wanted to know about Curtas.

Summary

Functionally the differences between this curta program and a real curta is that this program can output minutes and seconds and this program takes speeds as inputs whereas a real curta requires the user to set the sliders to the time to travel factor for the speed.

This program can

  • Compute time given a speed and a distance (the general goal)
  • Operate in either seconds or cents mode.
  • Accept start times
  • Easily compute times for one tenth and one distance unit increments and decrements.
  • The powerful calculator that the program is a part of can still be used while the program is running.

Things it doesn't do, that you might want it to

  • Truncate time values.  Times are shown carried out to more precision than you'll ever be able to use.
  • Hour roll-overs not correctly displayed.  The bottom of hour is displayed as 60 not 00.  The minutes count up like this: 58, 59, 60, 01, 02.  You understand.
  • Day roll-overs not handled.  Instead of rolling over to 0000 at midnight it keeps counting to 2400.  But according to the above issue it's not even 2400 at midnight it's 2460, nice eh? 

Basic Operation

The first step is to Clear the program using the "Clear" button and setting the units (seconds or cents) via the "Set" button.

The second step is to input an initial time.  This time will be the basis that all of your calculated times are added to. 

Next, a speed is entered using the "CAST" button.

Then distances are entered using either the "D" (the one on the top row) or any of the + or - buttons.  When a distance is entered a time is calculated and displayed.

Thereafter speeds and distances are inputted and times are calculated until you get tired of it and just tell the driver he's on-time and not to worry about it. 

Button by Button

The first row of buttons deals with distance input:

Button Input action Output Notes
+1 increment distance 1 unit calculated time  
+.1 increment distance .1 unit calculated time  
D input absolut mileage calculated time  
+1 decrement distance 1 unit calculated time  
+.1 decrement distance .1 unit calculated time  

The second row of buttons are more inputs:

Button Input action Output Notes
P/G input pause or gain calculated time  
CAST input speed time to travel factor  

The third row of buttons are all output, peaks at the current value:

Button Input action Output Notes
sp   current speed setting  
D   current distance  
t   current calc'd time  
u   units, 60 or 100  
d   delta dist.  used in last calc  

The third row of buttons are all output, peaks at the current value:

Buttons Input action Action
Clear -> yes   clears, time, distance, and speed
Clear -> no   nothing
Set -> D   set distance
Set -> T   set calc'd time
Set -> D   put program in cents mode (1/100ths)
Set -> D   put program in secs mode (1/60ths)
Set -> esc   nothing

Representations

Time is represented as hhmm.ssssss or hhmm.cccccc.  where h is an hour digit, m a minute digit, s a seconds digit, and c a cents digits.  As mentioned above the seconds or cents aren't truncated for you.

A Scenario for computing a leg

I'll use the first TSD section of 2002 Raindrop Rally which was Section #2 "OH! LA! LA!".  We'll pretend we'll car 11.  You'll want to hav the RI's in front of you.  (for a novice rally three casts and three turns in the first mile of TSD seems a little harsh, don't you think?)

 

  Numeric Input Curta Button(s) Displayed Output Comments
1 Clear      
    Clear, yes 0.000000  
2 Set units (1/60ths or 1/100ths of a minute)
    Set, secs   we'll use cents
3 Input the time of our first instruction
  1136 Set, T 1136 11:25 plus 11
4 Input the first CAST
  23 CAST 2.608696 60/23
5 Calc time for 2nd RI
  .14 D 1136.219130 that's 21.9 seconds elapsed
6 New CAST
  28 CAST 2.142857 60/28
7 Calc time for 3rd RI
  .45 D 1137.017702 1:01.7 minutes elapsed
8 CAST (again?)
  29 CAST 2.068966 60/29
9 Time for RI 4
  .96 D 1138.050805 pass the sign at 11:38:05
10 Time for RI 5
  2.6 D 1141.286667 11:41:28, no rounding
11 CAST
  34 CAST 1.764706 60/34
12 Time for RI 6
  3.95 D 1143.516079 pass the reference at 11:43:51.6
13 Calc intermediate time
  5 D 1145.427844 the mileage at 11:45:42.7
14 Time for RI 7
  5.91 D 1147.191373  
15 Time for RI 8, with fuck-up
  7.52 D 1150.096079 wrong mileage!
16 Fix fuck-up: look at what you entered, then fix it.
    D(3rd row) 7.52 that's not right!
  6.52 D 1148.237256 correct
  it's that easy, it's not much more difficult if there was a CAST involved.
17 Time for RI 9
  7.88 D 1150.477256  
18 Time for RI 10
  8.53 D 1151.565491  
19 CAST
  24 CAST 2.5 60/24
20 Why calc time for RI 11, skip it, calc the pause at RI 12
21 Time for RI 12
  8.8 D 1152.370491  
22 Pause 60 (seconds)
  60 P/G, pause 1153.370491 turn onto banner at 11:53:37
23 Time for end of Free Zone
  9.03 D 1154.115491 correct, but weird number
24 You know there will be √. (or two) in the next mile.  Calc intermediate times
    +.1 1154.265491 look at stack to see mileage
    +.1 1154.415491 mileage: 9.23
    +.1 1154.565491 another turn of the crank
    +.1 1155.115491 look a whole minute went by
    +.1 1155.265491 mileage: 9.53
    +.1 1155.115491 seen two √. so far, mileage: 9.63
    +.1, +.1 1156.115491 getting tired, mileage: 9.83
    +.1, +.1 1156.415491 mileage: 10.03
25 Time for RI 14
  10.17 D 1157.025491  
26 Kick it!
  44 CAST 1.363636 60/44
27 Time for RI 15
  11.58 D 1158.579127 again, a correct but weird number
28 Time for RI 16
  12.11 D 1159.412764  
29 Time for RI 17
  13.74 D 1201.546400 did you see the √.?
30 Calc an intermediate time
    +1 1203.164582 stack says 14.74
31 Time for RI 18, end of section, moment of truth
  15.12 D 1203.475491 subtract 12:03:47 from 11:36:00 (start time) gives you 0:27:47.  Wahoo!

 

Steve's Hints on Usage

(Always with the opinions that one is...)

I use a pen with a soft tip (either a gel ink pen or fine point razor type pen) when I'm calcing a rally.  It stands out better than pencil and I never make mistakes so I don't need to erase :)  Another advantage of the soft tipped pen is that I use pen as a stylus on the palm.  After a few pages of instructions you spit on the palm's scene and wipe the spittle and ink onto your drivers sleeve and keep calc'ing.

Links

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Gore

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Last modified: August 09, 2005
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