You can get more precise readings, by using smaller string, long ruler, and making better measurements. If you don't mind doing some math you can eas...
For all of us out there that just needs to measure their rocket fuel right now and can't wait. Or if you're like me who can't imagine spending money on a sale you won't use 99.9999% of the time. Here is how you can build one using your MacGyver skills and ordinary office supplies.
Step 1: Parts List
2 sheets of paper
2 large books