100829 Ruler Circular Calculator 300

The slide rule is brand new and well made. The instructions are in Japanese, but English versions are available by searching slide rule history sites. The scales are all standard, so any decent slide rule manual will provide needed how-to information.

The 28N is handy because it fits in a shirt pocket. The C and D scales are great for conversions and great for travel calculations (it is basically e6b flight computer pilots are trained on) this does come with English instructions. I also use this in the kitchen for doing unit conversions and scaling servings in a recipe. For example the recipe is for two servings and I want nine. I dial it in and can look up how much of each ingredient to use as I’m cooking (instead of stopping to pound out each conversion manually on a calculator).The 270 is a great slide rule. Unlike the 28N this has a great quality tactile feel. The english manual can be downloaded from the Slide Rule Museum website are really good. They go over some nifty tricks including ways to solve various trig problems.The 300 is of the same quality as the 270 but also has LL2 and LL3 scales. Everything is aligned properly. This is now my favorite. The trig scales are read differently on the 300 than the 270 so that may be why some people think it’s off. I just saw a video on youtube show how to use the log log scales to calculate interest. It’s neat because you can just lookup when it will double or triples. You can put the number of times it compounds per year as well. It’s much easier than typing in the compounding formula on a scientific calculator and gives a ton of results with one setting. Of course you can use them for other power and exponent calculations as well.

The Concise 300 is a seriously capable 4" circular duplex slide rule. Scales on the front are K, A, D, C, CI, B, and L. On the reverse are LL1, LL2, LL3,D, C, S, T1, T2, and ST scales. Scales are engraved, clear and well aligned. The central slide rings on both sides move smoothly, as does the cursor.I have tested its most basic scales and found them quite accurate, well aligned and easy to read. I'm not yet familiar with all the scales on this model but have no reason to doubt they are equally well executed.The construction is sturdy and should be durable.My one complaint is the instructions are only in Japanese. I was able to download a set of instructions in English from a third party site. Failure to include them with the rule as shipped is a deficiency because the Concise circular rule operates differently from others like the older Picketts, and has different scales arrangements that require some significant changes in how the rule is manipulatedThe size of the 300 makes it too large for most shirt pockets. But, it will fit in most larger jacket or suit pockets.Aside from the issue with the instructions, the Concise 300 isa very satisfactory tool, easy to set and read with good precision, well made and darned convenient.

Model 270NNot all circular slide rules are the same in which scales they have, and how these scales are laid out on the rule. I like this slide rule. In particular, I like the order of the scales on the front. The outer fixed ring is, in order, A - D, and the inner rotating ring is, in order, C - C1 - B - K and L, as one can see from the images. New users may not know why some think the ORDER of the scales are important. Because the A and B scales are identical and used the same way in finding squares and square roots, having them separately paired (A with D and C with B) makes it easy to use either the D or C scale for this function (scales D and C are also the same as each other).I also like that the log scale, L, is on the front. Many circular rules put it on the back with the trig scales so you have to flip it back and forth. On the 270, the back is angles: sines & cosines (S), tangents & cotangents (T1,T2) and the tiny angles (ST). The front side is multiplication, division, squares, square roots, cubes, cube roots, inverses of numbers and logs. Basically, math functions.At 4 inches this rule is pretty small, but not too small to hold and operate. On mine a light touch lets the inner rings, front and back, move smoothly. Too much thumb pressure presses them down onto the base and they turn stiffly. Some have found that at certain positions the numbers on C and D don’t line up. On my scale, they all do. For the price, I couldn’t be more pleased with this rule.

I bought this slide rule as a backup to the Picket and Keuffel and Esser slide rules I bought on eBay (both like new condition). I thought this slide rule would be cheaply made but its not, its made of thick durable plastic. What surprised me is that the Picket slide rule was impossible to read even with my glasses on and the Keuffel and Esser is very hard to read as it has very find lines. So this Concise slide rule turned out to be very readable and so much easier to use. It would be nice if Concise could make a regular slide rule rather than just a circular one as it would be much better than the old kind which were made of metal and wood. Some other reviewers of this slide rule said that the numbers dont line up and showed pics to prove it. I didnt not have that problem with the slide rule I got. So hopefully that was a temporary defect that they found and corrected.

This item is even better than the one that my Dad gave me back in 1973 as a pocket slide rule.I won't use it that much at home, but it will be part of my GTH kit - no batteries, little chance of breakage, and a wonderful way to quickly do certain field calculations in an emergency situation.