--- title: "Glossary | Once Books" description: "A plain-language glossary of the ideas behind consistent AI picture books: the Character Sheet, Identity Sheet, Consistency Engine, drift and more." source: "https://www.oncebooks.com/glossary" --- Glossary # The words we use A plain-language glossary of the ideas behind consistent AI picture books: the Character Sheet, Identity Sheet, Consistency Engine, drift and more. **answer key** The solution page for a puzzle, showing where each hidden word sits, so a reader can check their work. A word search book without answer keys gets returned. Our generator shades each hidden word in the solution, so the answer section is easy to scan. By default those answers sit at the back of the interior manuscript; the studio can also export them as a standalone answer-key PDF. **bleed** A small overrun of colour or art (0.125 inch) past the trim line, so a full-edge design still prints to the edge after the page is cut. Bleed only matters when something is meant to reach the page edge. A plain word search interior with white margins needs no bleed; add it only if a page carries a full-edge background, and then extend that art 0.125 inch past the trim on every outside edge. **Character Sheet** A locked description of a book’s hero (a written profile plus approved reference images) that every page is generated against so the character stays consistent. Image models don’t remember what they drew a moment ago. So Once Books re-supplies the Character Sheet on every page, and it stays the single source of truth for who the hero is. That is why a book reads as one book, not a set of loosely related pictures. See how it is built on [how it works](https://www.oncebooks.com/how-it-works), and read a finished result in the [sample books](https://www.oncebooks.com/examples). **Consistency Engine** The system that keeps one child recognisable across a whole book: locked character descriptions, reference images forwarded on every generation, and a single art style frozen onto the book. “Consistency Engine” is our name for the whole approach, not a single feature. It exists because statelessness (the model forgetting page to page) is the core reason most AI picture books drift. We pull the approach apart in [how the consistency engine works](https://www.oncebooks.com/blog/how-the-consistency-engine-works), and the [sample books](https://www.oncebooks.com/examples) show the result. **dot grid** A page ruling of evenly spaced dots, usually 5 mm apart, that guides writing, tables and sketches without printed lines. The standard ruling of a bullet journal. Dots are printed small (about 0.9 pt) and mid grey so they disappear behind ink. Our journal pages snap the lattice to the safe area so the margins are even. Print one from the [dot grid page](https://www.oncebooks.com/journal/dot-grid). **Drift** The gradual loss of consistency across an AI-generated book (the hero’s face, proportions or style changing page to page) that Once Books is built to prevent. Drift is the failure mode of naive AI books. Because each page is a fresh guess, the child from page one slowly becomes someone else. Locking the character and style is what stops it. [Why AI picture books drift](https://www.oncebooks.com/blog/why-ai-picture-books-drift) shows the failure up close, and the [sample books](https://www.oncebooks.com/examples) show it prevented. **Environment Sheet** Locked descriptors for a recurring setting (a bedroom, a wood, a classroom) so a place looks like the same place each time the story returns to it. Characters aren’t the only thing that drifts. Without a fixed environment, page three’s forest is a different forest by page nine. The Environment Sheet applies the same locking idea to places that the Character Sheet applies to people. The [sets gallery](https://www.oncebooks.com/examples) shows a recurring place held steady. **Generation Seed** The starting value we send with each image request. It steers the variation between takes of the same scene rather than locking an exact result. Image models start from a seed, and changing it gives you a different take of the same prompt. Our image provider treats the seed as a nudge, not a guarantee, so it is not what keeps a book consistent. That job belongs to the reference images and the frozen [Style Profile](https://www.oncebooks.com/glossary#style-profile), which are re-supplied on every page. **gutter margin** The inside margin nearest the spine, sized larger as page count grows so the binding does not swallow the content. A thicker book curves more pages into the spine, so the gutter has to widen with page count, from roughly 0.375 inch up to 150 pages to 0.5 inch or more above that. Getting it wrong is the most common reason a first puzzle book fails review. **habit tracker** A grid page for marking a daily or weekly habit across a month, one row per habit and one column per day, so a streak is visible at a glance. A common planner and journal page. A habit tracker turns a plain grid into a page with a job, which is what lets a title name a reader and a use. The [planner maker](https://www.oncebooks.com/planner-maker) can add a monthly habit tracker to a planner, and the guided pages in the [journal maker](https://www.oncebooks.com/journal-maker) include a habit grid. **hidden cube** A cube in a cube counting figure that is fully covered in the drawing by the cubes in front of and above it, so it must be counted by reasoning rather than by sight. Hidden cubes are how cube counting puzzles get harder. Our easy grade hides few or none, hard hides 40 or more, and expert 70 or more. Because every cube rests on another and the figure is one connected piece, a hidden cube can always be deduced from the column above it. **Identity Sheet** A character rendered once as a fixed, style-neutral reference that becomes the visual anchor every later page is generated against. Where the Character Sheet is the written description, the Identity Sheet is the visual anchor: one clear full-body rendering of the same face and build, re-supplied to the illustrator on every page so the likeness stays steady whatever the character is doing. You can see an Identity Sheet on [how it works](https://www.oncebooks.com/how-it-works). **interior PDF** The print-ready file holding every inside page of a book, sized to the trim, with fonts embedded, that a print service like KDP prints from. For a word search book the interior PDF is the complete manuscript: the puzzles first, then the answer section at the back, because KDP takes one interior file per book. The studio renders it at 300 DPI to whichever trim you choose. A standalone answer-key PDF is available too, as an optional export. **isometric drawing** A way of drawing a 3D solid on flat paper with the three axes at equal 120 degree angles, so the top, front and side faces all show in one picture at the same scale. Every cube counting puzzle is an isometric drawing, and every build-the-solid puzzle is answered on isometric paper. Nothing is foreshortened, so a cube reads as a cube wherever it sits, which is what makes the drawings countable and drawable by hand. **KDP trim size** The finished page dimensions of a printed book, for example 6 by 9 or 8.5 by 11 inches, chosen before layout so the interior and cover are sized to match. Trim size decides how much room a puzzle grid has. Large-print word search usually uses 8.5 by 11 or 8 by 10 inches so the grid stays readable. Pick one trim and design the whole interior to it. **low-content book** A book with little or no written manuscript, where the value is in the format: journals, planners, log books and puzzle books such as word search. In a low-content book the reader does the work, so producing one is about layout and format rather than writing chapters. Word search is one of the most durable low-content niches on Amazon KDP. **no-content book** A book whose interior is entirely blank or a single repeated ruling, such as a plain notebook, as opposed to a low-content book that carries light structure like prompts or planner grids. The line is loose but useful. A blank sketchbook or a plain lined notebook is no-content; a gratitude journal, a planner or a habit tracker is [low-content](https://www.oncebooks.com/glossary#low-content-book), because it carries prompts, grids or a date structure. Both publish the same way on KDP, and Publisher Studio makes both, from a blank page to a guided form. **orthographic views** The separate flat drawings of a solid seen square on from the top, the front and the side (a plan and two elevations), each a shaded grid showing where any part of the solid lines up. A view is a shadow, not a count: a square is filled if anything sits behind it, however deep. Draw-the-views puzzles ask for the three views of a solid, and build-the-solid puzzles run the other way, from the views back to the one solid that fits all three. **paper weight (GSM)** How heavy a sheet of paper is, measured in grams per square metre; heavier paper shows less ink through the page but adds a little to the spine. Print services offer a small set of paper stocks rather than a free choice of weight, so in practice you pick white or cream and the service fixes the rest. The choice feeds the [spine width](https://www.oncebooks.com/glossary#spine-width), because a thicker or heavier stock makes the same page count a little wider, which is why the spine is computed from the paper as well as the count. **print-ready** A file prepared to a print service’s requirements: correct trim, embedded fonts, 300 DPI, and bleed only where needed, so it can be printed without changes. Print-ready is the difference between a file that clears review and one that bounces back. A print-ready word search interior sits at the exact trim, renders crisply at 300 DPI, and pairs every puzzle with a readable answer key. **recto and verso** Recto is the right-hand page of an open book and verso is the left; a two-page spread opens with the verso on the left and the recto on the right. The distinction matters for anything drawn across two pages. A month or a week [spread](https://www.oncebooks.com/glossary#spread) has to open on a verso so both halves face each other, which is why the planner compiler slips a notes page in where a spread would otherwise land on a recto. Recto pages also carry the outside margin on the right, verso on the left. **Reference Image** One of the approved photos or renders that anchors a character’s appearance, supplied to the illustrator on every page rather than relied on from memory. Your uploaded photos become reference images. A few clear ones from a mix of angles give the illustrator enough to keep the likeness steady across the whole book. The [cast and sets gallery](https://www.oncebooks.com/examples) shows a few of these sheets. **spine width** The thickness of a book’s spine, worked out from the page count times the paper’s per-page thickness, which sets how wide the full cover has to be. Spine width is arithmetic, not a guess: the page count times the paper thickness a page, roughly 0.0025 inch for cream and 0.0022520000000000005 inch for white on KDP. Get it wrong and the title and art sit off-centre on the printed spine. The free [KDP cover calculator](https://www.oncebooks.com/tools/kdp-cover-calculator) gives you the number; Publisher Studio works it out from the final, evened page count and gates the cover on it, and drops printed spine text on books too thin to carry it. **spread** Two facing pages read as one: the left-hand (verso) page and the right-hand (recto) page. A month or a week laid across a spread must open on a verso, or the two halves never face each other. In a bound book, odd page numbers are on the right and even on the left. A planner spread placed on an odd page is split across a page turn. The [planner maker](https://www.oncebooks.com/planner-maker) compiles the book so every spread opens on an even page, inserting a notes page where it has to. **Style Profile** One art style, chosen once and frozen onto an entire book, so every page inherits the same look instead of being re-invented. The Style Profile is why page one and page twelve belong to the same illustrator. It is chosen before generation and applied uniformly, so there is no jarring switch from watercolour to a 3D render halfway through the story. Browse the [art styles](https://www.oncebooks.com/styles) a book can be frozen to. **undated planner** A planner with blank date fields the buyer fills in, so it sells all year and never expires, unlike a dated planner that prints the real dates and weekdays for one specific year. An undated planner is the safer first project: it has no season to miss and a listing accrues reviews for years. A dated planner converts better because the dates are done for the buyer, but it has to be live by October to catch the new-year rush. The [planner maker](https://www.oncebooks.com/planner-maker) compiles the same layout either way, and [dated vs undated planners](https://www.oncebooks.com/blog/dated-vs-undated-planners) weighs the trade-off. ## Keep reading - [The blog](https://www.oncebooks.com/blog) — Longer reads on how the books are made, what goes wrong in AI illustration, and how to choose photos, styles and formats. - [Answers](https://www.oncebooks.com/answers) — One sharply-scoped question per page, cost, safety, timing, printing, answered in a couple of sentences before the detail. - [Help centre](https://www.oncebooks.com/help) — Task-shaped instructions for making, printing and sharing a book once you have started one.