6.75 Calculations

[hardingjosh]

hi guys,

now i know you can do lots of calculations with the navitimer but what can you do with the Bentley 6.75? can't work out what the slide is trying to tell me!!! (probably as i'm a noob)!!

lots of numbers any meanings?

cheers

josh

[anton]

It's a Telemeter:

Timing to 1/5 second.

Timing up to 30 minutes.

Timing telephone conversations.

Tachometer scale.

Telemeter scale ®.

By means of the telemeter scale it is possible to measure the distance of a phenomenon which is both visible and audible. The chronograph hand is released at the instant the phenomenon is seen; it is stopped when the sound is heard, and its position on the scale shows at a glance the distance in kilometers or miles separating the phenomenon from the observer. (Calibration is based on the speed of which sound travels through the air, viz. approximately 340 meters or 1,115 feet per second).

During a thunderstorm the time that has elapsed between the flash of lightning and the sound of the thunder is registered on the chronograph scale as illustrated on the opposite side. The distance between the observation point and the thunderstorm, in this case, is 1600 meters.

On this dial there is also a tachometer scale, which is shown by blue circles (See number . This is used in the following way: if the minute-recording hand points to 0, the speed will be shown on the outer circle (speed between 1,000 and 60 kilometers); if the minute-recording hand points to 1 minute, the speed will be shown on the middle-circle (speed between 60 and 30 kilometers); if the minute-recording hand points to 2 minutes, the speed will be shown on the inside circle (speed between 30 and 20 kilometers).

[andreww]

I don't think that is correct Anton. The Breitling for Bentley site shows this model as being equipped with a Slide Rule, and a variable Tachometer.

[anton]

I don't think that is correct Anton. The Breitling for Bentley site shows this model as being equipped with a Slide Rule, and a variable Tachometer.

I am certain that the Bentley line is used to measure ground speeds; as opposed to the Navitimer, which is used to measure air speeds. And you're right, Andrew, that it is a Slide Rule in the sense that it could also be used as a rudimentary calculator.

I had a friend who used his navitimer as a Tip Calculator!

[andreww]

You are correct Anton. As I recall, the Bentley dial is set up to calculate automobile related calculations. Acceleration springs to mind.

[BobM]

But to use as a standard slide rule, the layout is confusing. The inner log scale runs 0 (beginnig at about 2:45) to 10 counterclockwise. The outer log scale runs 0 to 10 clockwise, such that the two log scales oppose one another, unlike a regular slide rule where both scalles run clockwise.

However, regular calcualtions can be made easily enough. Position the log scales such that 3 on the outer dial is over 2 on the inner dial. Look around to the beginning of the inner dial (the index of the inner dial) see the value on the outer dial is 6. 2 x 3 = 6. Without moving the scales, look at other relationships: 1.5 x 4 = 6, 3x2=6, etc.

Let's do 9 divided by some values ... aliign 9 on the outer dial with 1 (the index value) on the inner dial. Now look on the outer dial for, say 4.5. 4.5 divided into 9 should equal 2, right? Look at the inner dial under 4.5 ... it's 2. ... or, look at the vaues on the inner dial: 2 on the inner dial divided into 9 equal 4.5, the value on the outer dial bove 2.

So, playing around with these relationships on these "opposed" log scales, you can figure out how to multiply or divide anything by anything.

Faked me out a while, too, until I figured it out.

[drhydro]

The two scales on the Bentley are equivalent to the CI (C inverted) and D scales on a slide rule. The normal Navitimer has C and D scales. They aren't telemeter or tachymeter scales at all-

The earliest Breitlings with slide rules (the Chronomats) had the CI - D arrangement; it appears that the C-D arrangement appeared a bit later, in watches designed more for pilots- the C-D scales on the Navitimer series are set up just like the scales on the classic E-6B navigation computer. I haven't looked into this in great detail; think I'll go a-googling. I love my Navi and my Bentley Big Date. Platonically, of course.

[hardingjosh]

good work guys!!

bobm a ture gentleman and a scholar!!!! i can put my mind to rest now, its easy when you know how!

cheers

josh