The mechanical keyboards usually called as tenkeyless are standard keyboards which come in standard size and are developed without a number pad. Such keyboards are very handy for work areas which are small in size.
Tenkeyless boards are good for users who are not adept at using a tenkey keyboard. Mechanical keyboards are different from the most common 104-key keyboard with function keys, alphabets, arrows and number pad on it. Although this layout is very common type of keyboards, it is not ergonomic.
The recent ideal workplace PC standard for a workstation requires you to place your arms, wrists and hands in a straight line in front of you, shoulder width apart. Any angles in your wrist can cause excess strain which could lead to soreness or even carpel tunnel. For standard human size the normal keyboard is too wide when you have your left-hand position correctly on the home row and your right hand on your mouse, your right wrist will have to strain in order to reach the home row.
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If your right-hand position is correct, your left hand is too far to the left. To solve this problem, mechanical tenkeyless keyboards are introduced especially for gaming purposes. Tenkeyless simply means a layout that is missing the number pad and its modifier keys.
Without number pad in the way the user can shift the keyboard more towards the centre and have their wrists at a more pleasant angle. On a tenkeyless keyboard placing your left hand on WASD keys and right hand on the mouse, you will have a perfectly ergonomic setup.