Assuming that everything MECHANICAL (ie, camshaft, timing chain) is working properly: pull the #1 plug, put your compression gauge tube in the hole WITHOUT connecting the compression gauge (assuming you have a 2 piece compression gauge), put your finger over the hole in the compression gauge tube, turn the engine by hand, using a long rachet and socket until you feel the compression. At this point you have 2 options, slowly turn the engine by hand until pressure stops and you start feeling vacuum, then turn the rachet the other direction a couple times until you have split the difference between compression and vacuum. It's actually a pretty good guess, but if you can see the timing mark you can get it EXACTLY on TDC.
the piston in cylinder #1 at the top on the compression stroke
It is when the number one cylinder has reached top dead center on the compression stroke.
The compression ratio is calculated using the formula: [ \text{Compression Ratio} = \frac{\text{Volume of Cylinder at Bottom Dead Center (BDC)}}{\text{Volume of Cylinder at Top Dead Center (TDC)}} ] This ratio indicates how much the air-fuel mixture is compressed in the cylinder of an internal combustion engine, with a higher ratio generally leading to improved efficiency and power output.
That would be the top of the compression stroke on the number one cylinder.
The location of the ECU is in the engine bay dead center...
The TDC is when the number one cylinder is at the top or top dead center of the compression.
There is no direct connection between compression ratio and pressure. Ratio is a mathematical calculation of the cylinder volume from bottom center to top center. Actual cylinder pressure will depend on the volumetric efficiency of the engine. Factors the affect volumetric efficiency include rpm, intake design, throttle plate size, amount of restriction in the exhaust, size of the valves, shape of piston and combustion chamber.
Look at the distributor and make a mark on the housing where the #1 cylinder connects. Then pull the distributor cap. The mark is so you know where #1 is with the cap off. Next, bring #1 cylinder to top dead center on the compression stroke. The rotor should be pointing at the mark you made. If you need directions on how to get #1 to TDC on the compression stroke - another topic..
To determine if cylinder number 1 is on the compression stroke, you can perform a few checks: First, remove the spark plug from cylinder number 1 and put your finger over the spark plug hole while manually rotating the engine using a wrench on the crankshaft. If you feel air pressure pushing against your finger, the cylinder is on the compression stroke. Additionally, you can observe the timing marks on the crankshaft and camshaft; they should align according to the engine's specifications when cylinder number 1 is at the top dead center (TDC) on its compression stroke.
Yes
No, it is in crankshaft degrees, an example: intake centerline of 108* degrees, means the centerline occurs 108 degrees past Top dead center on cylinder 1.
This means the timing is set to fire the spark plugs at 10 degrees before top dead center on the compression stroke.