How it works · the pattern engine
How we check every pattern.
Every Purlgrid pattern starts as a chart. Our pattern engine writes the instructions from that chart, counts every stitch, and refuses to make the PDF until every check on this page passes. Below are the rules it uses, with the real numbers from our patterns, and the things it cannot check for you.
- 01The cast-on divides into everything above it.The stitch count of every size must be an exact multiple of the rib and of every chart repeat, so no motif is cut in half where the round joins. If the size you want does not divide, the engine moves to the nearest count that does and tells you how far that is from the target.
Heartfelt Reindeer Beanie: 112 (128, 144, 160) sts ÷ rib 4 and repeats 8, 16, 4
- 02At most two colours in any round.Fair Isle is knit with one colour in each hand. A round that needs a third colour is a design error, and the engine stops there.
Every round of every pattern: ≤ 2 colours
- 03Floats over 5 stitches are marked, over 9 are refused.A float is the strand carried behind the work while the other colour is used. Up to 5 stitches it is left alone. From 6 to 9 the chart gets a ◆ where you catch the strand. Longer than 9 and the chart is sent back to be redrawn. In the round the engine counts across the end of the round too, because the repeats sit side by side.
Beanie reindeer chart: longest float 9 sts · 14 catch points
- 04Decreases land exactly.Every crown decrease round removes the same number of stitches in every section, and every size ends on the same small number to draw up. The crown decreases every other round until about half the stitches are gone, then every round, so the top lies flat instead of pointing.
Beanie crown: 112 (128, 144, 160) → 8 sts in 20 (23, 26, 29) rounds
- 05C2C rows add up.For corner-to-corner crochet, every diagonal row is written out colour by colour, and the colour counts of each row must add up to the tiles in that row. The tile counts must follow the increase and decrease rules at both edges.
Reindeer Hearts blanket: 100 diagonal rows · 2520 tiles · 564 colour changes
- 06Sizes come from body measurements.Sweater sizes use the Craft Yarn Council's published body measurements, 25 sizes from kids 2 to men 5X. The engine checks the finished chest against chest plus ease, that the sleeve top matches the armhole, and that the neckband stretches over the head.
25 sweater sizes · neckband checked against head size
- 07Names have to fit before you knit them.A name is charted letter by letter and centred on the front. If it is too wide, the engine says so before you cast on, instead of you finding out at the last letter.
Classic stocking (80 sts): EMMA 23 sts wide fits; CHRISTOPHER 43 sts does not (front holds 36); it fits the Large stocking
- 08Yarn comes from the stitch count.Metres per colour are counted from the stitches themselves: about 3.5 stitch widths of yarn per stitch, 1.1 stitch widths for every stitch a float passes, the cast-on and the ends, plus a 10% margin (15% for a colour used only a little). It is an estimate and the PDF says so.
Beanie, adult M: 120 m Snow + 35 m Cranberry
A real check, pass and fail
Same reindeer, two answers.
Our reindeer is drawn on a 16-stitch repeat with small snow dots in the gaps. We tried it on a 20-stitch repeat first: the four extra background stitches stretch the floats between the reindeer. These are the engine's own results for both charts.
Printed in the PDF
The checks for one pattern.
The last page of every PDF lists the checks that pattern passed. This is the list for the Heartfelt Reindeer Beanie:
- Cast-on counts 112 (128, 144, 160) are exact multiples of the 4-st rib and of every chart repeat (8, 16, 4 sts).
- Every round of every chart uses at most 2 colours. Longest float: 9 sts; every float over 5 sts is marked for catching.
- Crown: 8 sections; each decrease round removes exactly that many stitches and every size ends with 8 sts.
- Finished circumference gives 3–11% negative ease across the listed head ranges.
- Total height is within 0.6 cm of the target for every size; at least 2 plain rounds separate the colourwork from the crown.
Honest limits
What the engine can't check.
Your own gauge
Every number assumes the gauge printed in the pattern. Knit a swatch in the round, wash it, and count. If you get more or fewer stitches per 10 cm, the size changes with it.
Yarn swaps
The yarn estimate is for the weight in the pattern. A different fibre or a fuzzier yarn can change both the gauge and the metres.
How you like it to fit
The engine checks the numbers against standard measurements and ease. It can't know that you like your hats slouchy or your sleeves long.
Knitting it
The engine checks the maths, not the experience of knitting it. Our patterns are engine-checked; when a pattern has been test-knitted by people too, its page will say so.
Corrections
Found a mistake? Tell us.
Corrections are listed here and on the pattern's page, with the date. No corrections have been reported so far (checked 11 October 2026). Write to support@hugosoftware.net with the pattern name, the size and the row.