Very big typo there on engine oil amounts.
Check out the amount required with and without an oil filter change!
Getting back to the subject at hand, which is valve clearance. You should note that the picture shows two sets of feeler gauges being used at the same time.
I myself and probably lots of others used to do my valves with one set of gauges swapping from front to rear and back again. I was getting different readings and was endlessly changing until I decided to do both sides at the same time. That is, either the two inlet or the two outlet valve clearances.
I was amazed at the difference to the bike. The idle was immediately better as well as the pickup from low revs.
The other thing I have done is to purchase the Würth feeler gauges. These gauges are single feeler gauges, which means that you require two 0.30mm and two 0.15mm feeler gauges. They are light, extremely easy to use and I think they have improved the accuracy with which I now set the valve clearances.
Not a cheap item, but if you service your own machine and work out the overall scheme of costs, then it's very small.
Mick.