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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:

The second row of buttons are more inputs:

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

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

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?)

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

• Curta Calculators
• RPN calculator

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Gore

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