TABULATORS can be found on many portable typewriters, and the vast majority of standards.  The tabulator is a device that allows the carriage to move directly to a pre-set point.  There may be multiple points, which are controlled by the setting of TAB STOPS.  On some machines, a DECIMAL TABULATOR is fitted which allows for column work; these will have multiple keys or in some cases a special lever to allow the carriage to fly to a given column on a record sheet and end up at, for example, the spot to type "10,000" or in that same column to start typing "100" -- so that the final digit is always in line tat the right of the column.  These are unusual on portable typewriters.

On portables, one of three general kinds of tabulator may be found (IF fitted at all.)  These are generally referred to as KEY-SET TABULATOR, MANUALLY SET TABULATOR (or just MANUAL TABULATOR) and FIXED TABULATOR (or, on some Remington machines this last kind is called a SELF STARTER and some collectors use that older term in place of "Fixed tabulator."
These three machines display different forms of Key-set Tabulator.  To the right, a Smith-Corona which uses a toggle device to the right of the keyboard; depression of one end sets a tab stop, and depression of the other end clears a tab stop (naturally this occurs at the exact point the carriage is sitting when the device is operated.)  Moving clockwise, we see an Everest, whose tab stops are set and cleared using a lever at the top right of the keyboard labeled + and - : you can see the small white ball on the lever's end.  Below, an Olympia SM-9 with tab set and clear keys located on either end of the space bar. 
Many typewriters, of all kinds, have tab set and clear buttons/keys/levers in other places, but the function is always the same.  SOME machines have a lever on the carriage that clears all pre-set tab stops at once.
Typewriters with manually set tabulator stops will have only a TAB key or perhaps decimal TAB keys visible on the front.  You must access the back of the machine to change tab stops.  You will see a slotted cross-member running left to right with a number of stops on it.  These may have rings on their ends and be totally removable, or in some cases they may be permanently mounted on the tab rack and you'll have to depress a button or the whole top or side of the stop to move it.  On some portables, the tab rack and stops are concealed behind a panel that flips down; on some standards, you can flip the paper table over to see the tab stops (and the margin set stops as well.
Royal No. 5 carriage details, including tabulator stops.

No. 1) is the paper table, which on this machine flips up and over to reveal carriage mechanisms.  2) is the TAB RACK on which are mounted six TAB STOPS.  3) is the MARGIN RACK, and the number "3" is actually right on top of the right side margin stop.  4) is the PAPER BAIL with two ROLLERS.  5) is the PLATEN.  6) is located at the print point, just below which is the V-shaped PRINT ALIGNMENT FORK or TYPE GUIDE which ensures alignment of type at the print point, and ensures that two type slugs cannot reach the print point at the same time.  Both sides of this are (7) the CARD HOLDERS, for holding cards or such right the print point where the bail will not suffice.
Rear of the MONARCH portable shown on the previous page reveals carriage details.  The word TAB is right on the tab rack, with five tab stops placed along it.  They pull straight up for removal and repositioning, as do the vast majority of such manual stops.  The word MARGIN is by the margin rack, with the left-side margin stop located nearby on the rack. 

As you can see, some machines can be set/reset from the front, while others require that you stand up and look over the top.
This very modern GENERATION 3000 machine has a tab key at the right of the keyboard, which is red.  On this machine, the tabulator stops are at fixed points in the carriage travel and cannot be changed.  You simply have to tab over to the desired place, and then use backspace or space to arrive at the proper position if not there.

Some machines have, in addition to a conventional tabulator, a paragraph indent key which simply moves the carriage a fixed number of spaces inside the left margin stop.  This "extra" feature is not necessary; just set a tab stop at the desired place, or use the tab key once on a machine with fixed tab stops.  In point of fact, for most modern writers, the tabulator is not required at all.
KEYBOARDS on most typewriters you'll see are called FOUR-BANK keyboards, as they have four rows of character (letter and number) keys.  These use a shift key to type in capitals, and to type the symbols printed on the uppermost row of keytops.  There are some other keyboard designs out there, which are quite independent of whether or not the character arrangement is in the time-honored standard QWERTY style.
A few examples of THREE-BANK DOUBLE SHIFT machines, on which each key types three characters (a letter, the capital of that letter and a number or figure.)  Starting from top left, moving clockwise:  Corona No. 3, Sun Standard No. 2, Bar-Let No. 2, Blick Universal, Oliver No. 9, Harris Visible No. 4, Emerson No. 3, Underwood Portable, Blickensderfer No. 8.
On the left:  An example of a machine with DOUBLE KEYBOARD, which is actually a more modern term for machines which originally were referred to as FULL KEYBOARD machines.  There is exactly one key for each character or number, and thus one type bar and one type slug for each character or number.  The lower-case letters are typed using the lower half, in this case (a Smith Premier No. 2) the white keys; capitals are the upper half of the keyboard, or the black keys.

The vast majority of modern authors will wish to acquire machines with the conventional four-bank single-shift keyboard.  It is the most familiar, and the easiest to use, especially if the author frequently transitions between different typewriters or between typewriter and computer.
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