The description of Handy Data Logger
Once you have recorded data, you can view it in tabular, calendar, or graphical form. Data can be viewed for a given month, year, or all years. The graph can display the data as a line or bar chart, and a linear trend line can optionally be shown over the top.
Note: When importing from a CSV file, the format should be the same as the files the app exports. There must be a single header line containing the field names, and the first 4 fields must be Year,Month,Day,Value (Where the Value field can have any name, such as Rainfall). Following this may be the optional Comment field.