There is a section I find very interesting that was inserted at the very beginning of the discussions on keys:

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  At the CW world speed championship , HST 2008, held in Pordenone (Italy) the Belarus team has presented a key which is actually a hybrid between a paddle and a sideswiper. With such key, the Belarus team has reached and surpassed the stunning speed transmission of 70 WPM. This key was later produced by Piero Begali i2RTF as the HST, it is actually a single lever paddle with lever and transmission designed in such a peculiar way that it could be classified as a fifth kind of telegraph key of its own.

How is the HST a single paddle with lever and "transmission designed in a peculiar way that it could be classified as a fifth kind of telegraph key" - the HST is a single lever paddle that can be switched into sideswiper mode, or is there more to this key?

Then later in the discussion under "SIDESWIPER":

The Sideswiper The Sideswiper The sideswiper was born in 1888; Bunnel marketed it under the name of "Double Speed". This rare kind of key was designed to cope with the need of finding a solution to the terrible phenomenon of the glass arm. Terrible, indeed, because it forced radio operators around the world to rest, unable to work, for a long time. The sideswiper offered a simple and straightforward solution: instead of moving vertically the lever moved horizontally, closing a pair of contacts, one at the right and one at the left. The history of this key practically ends here. The semiautomatic key was already under development and was going to be adopted soon. After Martin invented the bug, the sideswiper fell into oblivion. In the mid-50s, this key was renamed the "cootiekey" because of the mechanical simplicity that characterizes it. Mostly Russian radio operators for marine traffic, both military and civilian, have adopted this key. Today, in 2009, radio amateurs who use it regularly can really be counted on your fingers, so this type of key and its own manipulation techniques have been largely forgotten. 

The sideswiper is composed of a base, not necessarily heavy, with a central lever ended by a manipulation paddle, and two contacts. The electrical path can be closed either right or left. At first glance, one might think that you can mock-up a sideswiper with a single lever paddle. Actually, the two keys are very different. First, the fulcrum in a sideswiper is located at the opposite end of the paddle. Moreover, the sideswiper has a longer lever, which in a single lever paddle is mechanically shortened by the presence of the fulcrum right in the middle of the base. All these factors lead to a mechanical response of the paddle which predisposes it for use with an electronic keyer. 

The efficiency of this kind of key, however, is striking: you can easily transmit in the 30 WPM range with a modest degree of fatigue. Manipulation, in fact, is simply an alternation of your wrist from right to left, closing the contacts on either the right or the left side. Be the current element a dot or a dash, you simply keep alternating in a left/right fashion, always being careful to maintain the proper timing and spacing. The secret of this kind of manipulation is in the rotation of the wrist and in the correct spacing between the thumb and index finger, which allows a flight time consistent with the transmission speed. 

The sideswiper is commercially produced in series by GHD, while two Italian craftsmen make special versions of the sideswiper: Salvatore Canzoneri IK1OJM and Alberto Frattini I1QOD. Constructive solutions adopted originally by the original Bunnel key did not allow much variation, just the distance between lever and contacts. With the revival of interest in this type of key, the Italian craftsmen have been introducing technical improvements such as magnetic retention, a solution borrowed from the experience in paddle construction, and a very important  improvement for making manipulation easier and less straining. The sideswiper, in fact, has remained unchanged over the years thanks to its relatively low popularity among professionals, with the consequence that the initial design never developed as it would happen with a commercial product. 

The transition to a sideswiper is not easy, because it requires a manipulation style all of its own. It is important to understand the correct wrist rotation, which happens in such a way that is not comparable to the one adopted in manipulating a bug. With a bug, the wrist rotates along the axis of the forearm. With a sideswiper, the wrist alternates right and left using the wrist as a pivot. In other words the wrist "vibrates" right and left, leaving the thumb, index finger and middle finger describing an arc. 

The most complex aspect of using a sideswiper is the manipulation of dots and dashes, which may occur on either the right or the left contact. This type of key is a severe test for the radio operator because it shows, mechanically, that it is absolutely necessary to have mentally absorbed the proper timing and spacing. A paddle and a bug turn the difference between dots and dashes into a physical experience. That is, when we manipulate one of these two keys we instinctively associate the dash with the pressure of a paddle and a movement from right to left, and the dot with the opposite movement. The result of this manipulation is that the distinction between dots and dashes is physically manifested, because every element is supported by the experience of pressing the paddle in one or the other direction, causing a distinct perception of a dot and a dash. A more instinctive approach to radiotelegraphy, however, requires that these differences are blurred, or rather, the operator should have sedimented and acquired the sound of each element and the gesture of transmitting it in such a way that he simply forgets about them. The sideswiper is so hard to manipulate because it eliminates the very initial difference: dots and dashes are made during a constant left-right pendulum motion, and the manipulation becomes actually a modulation of the steady flow of alternate dots, dashes and the space between them according to the proper 3:1 timing and spacing. 

It is an approach much similar to that of the spoken word: the lungs emit the airflow, the vocal cords transform it into sound and the mouth modulates it into structured elements. With a sideswiper, the pendulum motion of the hand is the airflow of the lungs, the modulation of the mouth is given by the contact closure with the appropriate timing for dots and dashes, and the sidetone provides a voice to all that, as the vocal cords do. It is clear that undue concentration on only one of two elements, pendulum motion and duration of contact either right or left, is a serious obstacle to a proper manipulation. The secret is always the same: let your manipulation flow in accordance with the mechanical characteristics of your key. Simply keep trusting your automatic control mechanism, alternating the wrist and executing dots and dashes wherever they are found. Keep this motion fluent, listening to the feedback coming from the sidetone. 

It is advisable to approach the manipulation of a sideswiper this way: first build the instinctive pendulum motion, then differentiate it into dots and dashes. Start simply working out with your sideswiper, repeating a series of dots, each spaced exactly the same way: a dot of sound duration and a dot of space in between. Take a paddle with an electronic keyer, set a comfortable speed for you, between 15 and 20 WPM, and hold the dot paddle. Listen to the sound and replicate it using the sideswiper. 

Afterwards, do the same exercise with the dashes, feeling instinctively the 3:1 ratio and manipulating accordingly. Now press the dash side of your paddle and listen to the sound. Feel the difference. Finally, practice to transmit eight dots, four dashes, eight dots, always comparing the manipulation between the sideswiper and the paddle. When you feel confident enough, go ahead with your first QSO, the more QSOs you make, the faster will be your time in transitioning to the sideswiper. On the Internet, there is a group of operators who are reviving this kind of key: the Sideswiper Net. You can find them at this address 

Finally, a very Zen exercise: close your eyes, relax, shut down the sidetone volume completely and start manipulating by sending the first thing that comes into your mind. A correctly spaced manipulation of a sideswiper is pure meditation. It's all in the head, the sidetone is not needed.   

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