3.2.2. Usability
The two graphics libraries, AChartEngine for Android and Coreplot for iOS, provided appropriate facilities for these apps and
performed adequately when displaying files with several thousand
points. Both Android and iOS apps reacted responsively to drag and
pinch interactions
least squares approximation and Chebyshev approximation [29].
The least squares approximation minimises the average error in the
approximation whereas the Chebyshev approximation minimises
the maximum error and reduces the risk of significant localised
error. Both performed well for polynomials up to order 5, but as it
avoids the potentially ill-conditioned numerical matrix inversion
used for least squares approximation, the use of the orthogonal
Chebyshev polynomials [30] means that any order of approximation can be robustly computed