Check your instruments every month or so. Easier said then done but in the end, not wasting a batch of beer is worth the trouble.
Recently, I was brewing a beer of OG 1.048 but after lautering, the gravity of 15 liters of wort was 12 brix or 1.048. After boil, the volume would shrink to 10 liters and that would concentrate the sugars. In the end, I ended up with a beer that was 17.2 brix or 1.069. From a medium strength ale to a strong one! For this one, it wasn't the weighing scale but my brain that needed calliberation!! (concentrate while measuring). I added perhaps 50% more grain which was evident in the thick mash I got.
What could have I done or what I did that saved the day...
I could have boiled and re-diluted (with degassed boiled water) and made 15 liters but in the end, I just made a strong beer. However, I did add more hops to balance the sweetness, areated more to get enough O2 in the beer and pitched higher to ensure effective fermentation.
I am sure it will turn out to be a good beer. The best part: it will last for ages due to high alcoholic strength.