Three colors of wool are needed. The yarn amounts are given in ounces: 8 ounces of the main color, 7 ounces of the second color and 2 ounces of the third color.

Shetland 2 ply jumper yarn knits as 4 ply weight, aka fingering.

The body is knitted in the round until you divide for the armholes and knit the back and fronts flat up to the shoulders. The shoulder seams are joined with Kitchener stitch or a three-needle bind-off. Then the neckband is knitted. Finally, the sleeves are knitted top down, in the round.

If you don’t consider joining the shoulders as “seaming”, then this could be considered a seamless knit.