You’re given a grid that has been divided into areas. Fill each empty cell with a number so each area of size N contains one instance of each number between 1 and N. Depending on the game mode, the following rule is added:
On a touch screen, a tap does what a click does, and a long press what a right-click does (more ways to right-click). A key the puzzle’s controls show as a button can be pressed there instead of on a keyboard.
Left-click to select a cell, then type a number on your keyboard to enter it. A number larger than the cell’s area is not accepted. Press Backspace, Delete, Space or 0 to clear a cell.
Right-click a cell, then type a number to add a pencil mark. Pencil marks can be used for any purpose. Pencil mode is sticky: once a right-click switches it on, it stays on wherever you click, until you right-click again. The Marks key is lit while it is on, and pressing the key also switches it. To have it last only until your next click, turn off Right-click toggles a sticky pencil mode (stays on until right-clicked again) in the preferences.
You can also use the arrow keys to move the selected cell around. Press Enter to toggle between entering numbers and entering pencil marks.
Press Fill marks among the puzzle’s controls to write in every pencil mark wherever nothing is placed and no mark is written yet. The M key does the same, on any board where M is not something you type. Marks you have narrowed are left alone, and pressing again never starts over: see Filling in all the pencil marks. A cell’s marks are the numbers from 1 to the size of its area. Once every empty cell has marks, the press crosses out of each the numbers already placed in its area, and the ones a placed number is too near for.
Seismic mode is an implementation of Hakyuu, a puzzle invented by Nikoli. It’s also known as Ripple Effect. More information: http://www.janko.at/Raetsel/Hakyuu/index.htm
The inventor of Tectonic is unknown.
Hint explains the next step rather than simply making it. It works from your own pencil marks, and a cell with none counts as holding every number its area and the numbers near it haven’t ruled out yet, so an Easy board needs no marks at all. When a step reasons from a cell’s possibilities, the hint writes that cell’s marks first. If you would rather it start by filling in every cell’s marks (the same as pressing Fill marks), set Hints pencil in to Every candidate first in the preferences. As long as none of your marks has crossed out a cell’s answer, it carries on from wherever you are.
Most steps are the plain rules at work: a cell with only one pencil mark left, or a number with only one cell left to go in within its area. On Normal boards one more idea appears. When every cell an area has left for some number is close enough to a cell outside it to clash, that cell cannot hold the number: whichever cell the area uses, the two would break the keep-apart rule.
These parameters are available from the ‘Custom type…’ option on the ‘Type’ menu.