Shim

The goal

Every puzzle starts with fixed blocks (double border) and ground. Add blocks until every block is supported, the fixed ones included, using as little weight as you can. Your score is the weight you add: lower is better. A finished puzzle earns stars: ★ for solving it, ★★ at the best score, ★★★ also with the fewest blocks, and ★★★★ also in the smallest space (the smallest box around the whole building). Stuck? Click the stars at the top for what the next one needs, and to reveal its goal. In this lesson, you'll see how close you came: Great within 1, Good within 5, Okay within 25%.

The rules

A block is supported when the weight holding it up is more than its own:

• Gravity: the heaviest block right beneath it counts. Under one end is enough.
• Pressure: blocks on both sides, straight across, add their weights.
• Gravity and pressure add up.
• Congruent instability: a block touching a block of the same type, side by side or end to end, is never supported (a red line shows where they meet). Corners may touch.
• The ground holds anything. A red X marks a block that isn't supported.
• No block can go on a hatched square, and a hatched square holds nothing up: it's empty.

Mouse or touch

• Drag a block from the palette onto the board (R turns it while you drag). Or pick one in the palette, press on an empty square, and drag into the next square.
• Drag a placed block to move it; drop it off the board to remove it.
• Click a block's right or top half to make it heavier, its left or bottom half to make it lighter.
• To rotate a block, press one of its squares and nudge it sideways (across the block): the pressed square stays and the block turns to lie toward the side you nudged, or further round if something's in the way. Dragging further moves it instead.
• To work on several blocks at once, press an empty square and drag two squares or more away: a rectangle selects every block it touches. Beside the selection, pick whether dragging it moves or copies it, or flip it left to right. Click an empty square or press Esc to clear the selection.
• ↶ undoes your last change, back to the start, and ↷ redoes it. ↻ starts over (that can be undone too), ? replays this tutorial, and the grid button lists the puzzles.

Keyboard

• ←↑→↓ move the cursor's ringed square; with Shift, move the block under it.
• 1 2 3 4 8 H (½) place a block, or change one.
• R / Shift+R rotate clockwise / counter-clockwise about the ring.
• Space or Delete removes a block; Esc hides the cursor.
• Ctrl+Z (⌘Z on a Mac) undoes; add Shift to redo.