My question is, what defines a proper clearance measurement? I am doing my first valve adjustment of my life, learning as I go, and I am encountering varying degrees of clearances, and resistance to the gauges. If a gauge can be pushed in period, would that gauge size be the proper measurement? For example, say I hypothetically could not fit, no matter how hard I pushed, a .15mm gauge, but I could fit a .14mm gauge, albeit with a good degree of sticking and resistance, would the correct measurement of the clearance be .14mm? Or, is the proper measurement when you encounter no resistance to one gauge, say a .12mm, then a slight bit of resistance and contact with a .13mm, and then more significant heavy rubbing with a .14mm. Would the correct measurement be .13mm because it was the first gauge to encounter resistance?