Generally, you do not need to take care for the labels. GraphView will automatically generate and format the labels for you, so that the float-numbers won't get too big. However, you have the option to change how the labels are generated. For this, you have to set your own label formatter to the GridLabelRenderer. The most simple way is to change the number format. For this you can use the DefaultLabelFormatter and pass your date formats as arguments.

NumberFormat nf = NumberFormat.getInstance();
nf.setMinimumFractionDigits(3);
nf.setMinimumIntegerDigits(2);

graph.getGridLabelRenderer().setLabelFormatter(new DefaultLabelFormatter(nf, nf));

You can do a complete custom label generation. For example if you want to use a suffix like a currency. To do so, you have to implement the LabelFormatter interface or extend the DefaultLabelFormatter and override the formatLabel method.

// custom label formatter to show currency "EUR"
graph.getGridLabelRenderer().setLabelFormatter(new DefaultLabelFormatter() {
    @Override
    public String formatLabel(double value, boolean isValueX) {
        if (isValueX) {
            // show normal x values
            return super.formatLabel(value, isValueX);
        } else {
            // show currency for y values
            return super.formatLabel(value, isValueX) + " €";
        }
    }
});