Name: Slide Rule
Rating: 5 (1 reviews)
Author: 3igen3ggy

Have you ever heard of a slide rule? If yes, you might want to check this app. If no - I got you covered. 

Slide rule is a kind of an ancient calculator that engineers long time ago used to for example put a man to the Moon. Needless to say its a powerful tool, but its usage comes with a price. You first need to learn how to use it, and its not that easy. 

First of all, slide rule with its default scales (C & D) allows for easy multiplicaiton and division by adding and subtracting distances (thanks to logarithms properties). Secondary, with usage of additional scales (when being on particular scale hold menu button to show all possible scales like sine, hyperbolic tangent, logarithm etc.) slide rule works like a mathematical tables. On usual slide rule accuracy is up to 3-4 digits, here it is most often 7 digits. Some scales have "left-arrow" indicator (its sign is not allowed in description, so I can't explicitly write it here). This means the values of scale decrease, as you increase x. Also some scales like "T" for tangent are split into two "T1" for values of tangent [0, 1) and "T2" for values of tangent [1, 10). If you move "I" scale, the "II" hairline reading changes. If you move hairline (being focused on either "II" or "III"), the other one of hairline scale changes as well.

If you set slide rule as in the picture, you can calculate for example 12 * 25 = 300. Please be advised that there is no decimal point on these scales. You can move them within range [1, 10), but its up to you where decimal point is. Calculating 1.2 * 2.5 = 3.0 and 12 * 25 = 300 is done with the same setting, and its your job to be aware if result is 0.3, 3, 30 or 300. And that's beauty of slide rule.

Well, using actual slide rule tool is for sure easier than using digitally simulated one on your smartwatch. To make things worse, the resolution that Instinct operates on doesn't allow you to simulate a visual representation of slide rule, where something actually slides. You have to operate on three sets of scales, which readings (if you know what slide rule does) imitate what you could read off an actual rule!

If you don't have a slide rule, you might want to print/buy one (or download an app on your phone) and first learn using the real one, then you won't be that mad at this app for showing you some random numbers.

At the bottom the arros is shown, to let you know how the slider is moved (left or right). If its to right, you need to remember to move decimal point when multiplying or diving.

Here are constants that can be chosen from menu (and they often appear on slide rules): 
π = 3.141592, 
1/π = 0.318310, 
e = 2.718281, 
1/e = 0.367879, 
ρ = π/180 = 0.017453, 
ρ° = 180/π = 57.29578, 
ρ' = 180/π * 60 = 3437.747 , 
ρ" = 180/π * 60 * 60 = 206264.8, 
C = sqrt(4/π) = 1.128379, 
C1 = = sqrt(40/π) = 3.568248.

Why did I create it? Well, some usual watches come with a moving bezel with logarithmic scale on it that works as a slide rule (you might want to google it) so you have a mechanical calculator on your hand. Sadly, Garmin watches doesn't have such series. But then I thought - wait, you can program whatever you want on these! So I eventually did it. Will I ever use it for some kind of calculations? I am looking forward to it, but well, probably not. However I did this app and wanted to share.
