With the advent of computers, computations can now be achieved at very large digits of numbers. Calculators can also achieve large digits of numbers. When does one roundoff? What are significant figures? This chapter introduces the concepts of significant figures then proceeds to error propagation. Error propagation is a concept where some errors in measurable elements such as distances and angles eventually seep to the computed values such as coordinates/positions. We show in this chapter how these errors are propagated and eventually the analysis of their impact. An understanding of error propagation is must to be able to comprehend the final outcome of the processed data.