Short answer
Standing pressure is the pressure with no gas flowing; working pressure is the pressure while appliances are running. On a typical UK low pressure natural gas supply, the meter regulator is set to give about 21 mbar at the meter outlet, and working pressure at appliance inlets should stay within the appliance manufacturer's stated range under full load.
Measuring correctly
Measure standing pressure at the meter outlet test point with everything off, then working pressure at the same point with the largest load (ideally all appliances) running at full rate. Then measure working pressure at the inlet of the furthest or largest appliance. The difference is your installation pressure loss.
What the readings tell you
A high standing pressure with a big drop under load suggests a restricted meter, regulator or service. A normal meter outlet working pressure but low appliance inlet pressure points to undersized or obstructed installation pipework. Low standing pressure suggests an upstream supply or regulator problem.
Medium pressure supplies
Larger sites may take gas at medium pressure (above 75 mbar) and regulate down on site. Each regulated section then has its own MOP and working pressure, and the test points and readings must be identified for each.
Figures are typical for UK natural gas. The current edition of the relevant IGEM standard and the manufacturer's instructions always take precedence on site.
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