The actual needles used are 20mm not 19mm!

Gauge: there are three different gauges used here
· Double yarn on 20mm: 4 x 5 in 10cm x 10cm
· Single yarn on 20mm: 5 x 7.5 in 10cm x 10cm
· Single yarn on 15mm: 7.5 x 10 in 10cm x 10cm