There is a standard for meter accuracy. Off the top of my head I think they have to be accurate to within 5%, 85% of the time.
Please note that random testing won't show you anything meaningful. The regime that's generally followed is to test on waking (a fasting test, as you won't have eaten or drunk anything overnight), just before a meal and then 2 hours later. The difference between the pre-meal and post-meal reading should ideally be less than 3. If it's more then there were likely too many carbs in that meal and adjusting portion sizes might be required. If you record your results (I use a spreadsheet) then after a while you'll be able to see whether your BG is trending downwards (good), upwards (not so good) or is pretty flat. The target ranges are between 4 and 7 fasting and pre-meal, and less than 8.5 post-meal.
For anyone new to self-testing this is worth looking at:-
Knowing your blood sugar levels helps you manage your diabetes and reduces your risk of having serious complications – now and in the future. What are blood sugar levels? Your blood sugar levels, also known as blood glucose levels, are a measurement that show how much glucose you have in your...
www.diabetes.org.uk