TDC is 0 degrees TDC, not 10 degrees BTDC which is before top dead center. ATDC is after top dead center. Both of these in relation to piston height are "below top dead center".
top dead center is what it stands for. top dead center
The top dead cente
The top dead center is when the piston has reached its peak and can go no farther up, it has reached its summit. The bottom dead center is when the piston is at its lowest point.
looking at the timing marks from the top left to right you have 5 degrees after top dead center, then top dead center then 5 degres 10, 15 then 20 befor top dead center. the timing is 7 degrees before top dead center
wire that as number one or pull dist. and fix.
Each cylinder has a top dead center position.
TDC would be "Top Dead Center". BTDC would be "Before Top Dead Center".
It is when the number one cylinder has reached top dead center on the compression stroke.
top dead center
After Top Dead Center.
top dead center