Toshi, also please note that there are different standards of grading sandpaper. The European FEPA/EURO standard sandpapers always have a P in front of the grit value e.g. P400. The American ANSI/CAMI standard papers don't. The two different standards differ somewhat once the grit number goes above 220, with the CAMI standard grits being finer than the FEPA equivalent grit numbers. Note also that Micromesh products have a very different grit grading system to either of the above systems.
Here's a link to a comparison chart. https://www.thesandpaperman.com.au/a...ion-chart.html
Australia seems to use EURO/FEPA graded sandpapers, as do we here in the UK, but I don't know what the typical sandpaper available in Singapore is. I'm sure there are some areas of the world where both are available.
But on this forum, most people will be referring to EURO/FEPA graded sandpapers, with a P in front of the grit number, so when someone says 'sand to 400 grit', unless they obviously live in North America, assume they are talking about P400 grit - equivalent to ANSI/CAMI 320 grit.
So just check on the back of the sandpaper you're using, and whether the grit number has a 'P' in front of it. Whilst there is only a very slight difference at the 240 grit level, as the grit numbers go higher, the difference becomes greater e.g. an ANSI/CAMI 400 grit is significantly finer than a EURO/FEPA P600 grit paper.