Flag of Tuvalu — construction sheet
Own work. This construction sheet is based off of the description and flag image found in the Tuvalu National Flag Act.

1. The Tuvalu National Flag has an azure blue background with nine yellow stars lying diagonally across the right side from the top right-hand corner. In the top left-hand corner is the Union flag.
2. The proportions of the flag are —
(a) Width: Height - 1:2
(b) Area covered by Stars: One half
(c) Width of each star: Approximately 1/12 width of the flag

(d) Area covered by Union flag: One quarter.— Tuvalu National Flag Act 1997 (Revised 2008) — Schedule 1

The text portion of the Flag Act (Schedule 1) does not specify the precise location of the stars.
The flag image is in Schedule 2 is a simple low resolution bitmap image of the flag; it is not a specification drawing and it contains no text, but it does give us a reasonable idea of where each star is supposed to be located and how each star is supposed to be oriented.
The Flag Act can also be seen at paclii.org. That web page does not display the flag image, but there is a download button in the menu that sometimes works.  When the site is working, it will allow the download of a file named tnfa212.rtf. That file contains both schedules (including the image).
Neither of the websites referenced above belong to the government of Tuvalu, but since they both show the same image, one can assume that the government of Tuvalu did actually choose that specific image for the Flag Act.

There is an error in the Flag Act regarding the width each star.  It should have read 1⁄12 length of the flag instead of 1⁄12 width of the flag.  Otherwise the stars end up half the size of what is shown in the image.
The Flag Act does not mention imaginary circles around the stars, so the width of each star is assumed to be the width between two alternate points.  This definition appears to match what was used in the flag image in schedule 2.
Some of the stars may look to be placed at a very small (and very insignificant) oblique angle; this is mostly likely explained by pixelation and the general low resolution of the image.  It is assumed that all stars are supposed to have one point that points either directly up or directly down.

Rumor tells us that the layout of the stars is based on a map of the islands (with North pointing to the hoist). While this is likely true, it is not at all accurate.  If it was done perfectly it would require bunching and overlapping of some of the stars.

The image in the Flag Act was not created by the government of Tuvalu. It was originally created by vexillologist Željko Heimer and displayed at Flags of the World (FOTW). The image predates the 1997 Flag Act because the same Flag had been used by Tuvalu in 1978.  Thus it appears that in 1997 the Tuvalu government simply lifted an historical reference image from FOTW and stuffed it into an amendment for its Flag Act.
On April 11, 1997 when the amendment entered into force, Željko Heimer's flag image became part of the legal definition of Tuvalu's flag.
The image was replaced on the FOTW website in 2009. The reason for this is not entirely clear but it does mean that since 2009 FOTW has been displaying a flag that does not match the image in the Flag Act. Oh well.
FOTW has a mirror site that has not been updated since 2004; it still shows Željko Heimer's flag image. Five Star Flags.

The stars on this flag construction sheet are laid out to match Željko Heimer's flag image as it appears in the Flag Act and at Five Star Flags.  The version at Five Star Flags was used for measurements because it suffers from less compression artifacts.
Coordinates are rounded to 1⁄120 of the hoist because the reference image is not of sufficient resolution to justify higher precision.
The width of each star on this construction sheet (measured between two alternate points) is set to exactly 1⁄6 of the hoist (or 1⁄12 of the fly).
No stars are set at an oblique angle.
To simply reconstruction, imaginary circles are shown around the stars, the diameter of the circles has been calculated with trigonometry; the formula and the value are displayed under the Union Flag.
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