Original Problem: sin(45)(425N) + sin (60)(601N) = 821N The problem is, no scale is perfect. Let's assume for the time being that the angles are quite accurate, but you know based on your past experience that these scales can be off by as much as 2 N. This uncertainty propagates through any calculation that involves the measured quantities. By how much (in N) could your estimation of the weight of the box be off? Hint: The easiest way to do this is by finding the highest and smallest possible values of the weight that can result from the range of values of the measured forces. What I'm doing - but wrong answer: sin(45)(423) + sin(60)(599) = 817.8553853 sin(45)(427) + sin(60)(603) = 824.147914 Subtract higher from lower = 6.29300 Where am I going wrong?