There you go, notice the hole in the upper corner that was connected to a wire "cable".
Also notice the input BTU on the tag; 22,500 and 25,000. That is how much the main burner orifice allows through at any given pressure. System pressure from regulator at source is set at 11 inches water column (WC) this is about 1/2 psi. The regulator on gas valve you were asking about controls the pressure through valve to main orifice. Is doesn't reduce pressure much, so many times it is not visible looking at flames. You can normally hear a slight change in gas flow when you adjust it up and down. The only way to be sure would be a IR (infra red thermometer) checking surface temp on the top. Let it on high about 30 minutes, take a reading and let it on low about 30 minutes and compare readings. It should be slightly lower. To give you an idea of BTU, the difference is about what one stove top burner would be on a small burner of a gas kitchen range. More like a simmer burner.
They don't reduce the flame much since a direct vent appliance relies on the flow moving up and out of the exhaust. This flow creates a low pressure area or slight vacuum in the burner chamber which atmospheric air pressure outside PUSHES into the air intake allowing oxygen into the burner. So reducing the exhaust flow reduces the incoming air, which creates a richer air fuel mixture capable of sooting up glass, logs, exhaust, among other problems.
To test the regulator on valve, a manometer (very low pressure gauge) is connected to the orifice to test pressure. The result of turning that control up and down is so minimal, simply leave it on high is my recommendation. (I'm retired from my own propane service business of over 25 years) I've seen many that did very little. Again, listen carefully, if the sound changes from min to max, it's making a difference.
** Notice the label states at the bottom; "removal of this label will void compliance". Codes require certification and testing labels to remain attached to the appliance. Removing any label looses the testing certification, so a tested appliance using UL standard testing criteria is no longer "Listed" which no longer allows it's use. Just like removing a Vin number from a vehicle, it is no longer legally usable. That tag should be attached with a metallic cable or wire (copper is better than nothing) to the appliance wrapped around and tightened on a screw. (stainless is used to avoid melting in a fire) The serial number is stamped into the metal instead of a sticker, also in case of fire. (codes require it to be stamped or engraved) **
Many manufacturers have gone to larger tags so you can see them better when lighting than a sticker applied on the appliance where it is hard to see.