The Float data format is only valid up to 7 significant digits. Beyond this, round-off errors will occur and you will likely see some of the values change from their original values. To avoid this, use the Double format which is valid up to 16 digits. You need to change the format before opening, pasting, or typing the data. This can be set as a default in the Preferences dialog.
KaleidaGraph is a thoughtfully designed graphing and data analysis application for research scientists, as well as for those in business and engineering fields. It produces publication-quality graphs, and easily converts the most complex data into a functional display.