Camshaft degreeing inch to mm

Hi guys.

I have a little question about the cam degreeing course.

In the module about cam chart Andre talk about cam duration in inches and mm.

For my sr20det I have a camshaft chart listed in inches (duration 226° at 0.050" valve lift) but I'm using a metric dial gauge.

Should I measure the open and closing events at 1mm as said in the course?

I don't understand why I cannot juste make the conversion from inch to mm and measure from 1.27mm?

I've tried to measure it from 1.27mm and indeed it's never right. I should have : e.o at 49°BBDC and e.c at 3° BTDC but the valve is closing way before.

Is this because I'm not measuring it at 1mm?

I didn't try it at 1mm yet, but just wanted to know why we cannot just make the conversion for this process?

Thank you in forward for your answer,

Kind regards

Séverin

Here can you find the cam chart