I've did a bit of teorycrafting and looks like you have some issues with numbers between -1 and 1. Or what's it's the same with Numbers around 0. Where the logarithmic function returns negative values.
A logarithmic function has negative values around those values, so the error seems in that mathematical function. I'm GUESSING the problem is a sign problem Around those values.
I'm just guessing by the results and the data, since I do not have the matematical function you're using. But after thinking on it. I think it should be something around that.
But doing some research with google play ground I added to the upper values 1.3 to make all the values positive and the chart looks great
here you have the code:
function drawVisualization() {
var object = {cols:[{label:'date',type:'date'},{label:'',type:'number'}],rows: [{c:[{v:newDate(2007,08,27)},{v:2.2}]},{c:[{v:new Date(2007,09,24)},{v:2.2}]},{c:[{v:newDate(2007,10,21)},{v:2.1}]},{c:[{v:new Date(2007,11,21)},{v:1.9}]},{c:[{v:newDate(2007,12,23)},{v:1.9}]},{c:[{v:new Date(2008,02,29)},{v:1.9}]},{c:[{v:newDate(2008,03,25)},{v:1.6}]},{c:[{v:new Date(2008,04,23)},{v:1.8}]},{c:[{v:newDate(2008,05,30)},{v:1.8}]},{c:[{v:new Date(2008,06,25)},{v:1.7}]},{c:[{v:newDate(2008,07,29)},{v:1.5}]},{c:[{v:new Date(2008,09,01)},{v:1.2}]},{c:[{v:newDate(2008,09,24)},{v:1.0}]},{c:[{v:new Date(2008,10,26)},{v:0.8}]},{c:[{v:newDate(2008,11,23)},{v:1.0}]},{c:[{v:new Date(2008,12,23)},{v:0.8}]},{c:[{v:newDate(2009,01,25)},{v:0.5}]},{c:[{v:new Date(2009,02,28)},{v:0.0}]},{c:[{v:newDate(2009,03,24)},{v:0.0}]},{c:[{v:new Date(2009,04,22)},{v:0.1}]},{c:[{v:newDate(2009,06,01)},{v:0.1}]},{c:[{v:new Date(2009,06,24)},{v:0.3}]},{c:[{v:newDate(2009,07,28)},{v:0.7}]},{c:[{v:new Date(2009,08,30)},{v:1.1}]}]};
var data = new google.visualization.DataTable(object);
var annotatedtimeline = new google.visualization.AnnotatedTimeLine(
document.getElementById('visualization'));
annotatedtimeline.draw(data, {'displayAnnotations': true});
}
Finaly just inc ase I did a new try now with negative values all smaller than -0.9 and again the graphic looks great.
Here you have the code.
function drawVisualization() {
var object = {cols:[{label:'date',type:'date'},{label:'',type:'number'}],rows: [{c:[{v:newDate(2007,08,27)},{v:-2.2}]},{c:[{v:new Date(2007,09,24)},{v:-2.2}]},{c:[{v:newDate(2007,10,21)},{v:-2.1}]},{c:[{v:new Date(2007,11,21)},{v:-1.9}]},{c:[{v:newDate(2007,12,23)},{v:-1.9}]},{c:[{v:new Date(2008,02,29)},{v:-1.9}]},{c:[{v:newDate(2008,03,25)},{v:-1.6}]},{c:[{v:new Date(2008,04,23)},{v:-1.8}]},{c:[{v:newDate(2008,05,30)},{v:-1.8}]},{c:[{v:new Date(2008,06,25)},{v:-1.7}]},{c:[{v:newDate(2008,07,29)},{v:-1.5}]},{c:[{v:new Date(2008,09,01)},{v:-1.2}]},{c:[{v:newDate(2008,09,24)},{v:-1.0}]},{c:[{v:new Date(2008,10,26)},{v:-1.8}]},{c:[{v:newDate(2008,11,23)},{v:-1.0}]},{c:[{v:new Date(2008,12,23)},{v:-1.8}]},{c:[{v:newDate(2009,01,25)},{v:-1.5}]},{c:[{v:new Date(2009,02,28)},{v:-1.0}]},{c:[{v:newDate(2009,03,24)},{v:-1.0}]},{c:[{v:new Date(2009,04,22)},{v:-1.1}]},{c:[{v:newDate(2009,06,01)},{v:-1.1}]},{c:[{v:new Date(2009,06,24)},{v:-1.3}]},{c:[{v:newDate(2009,07,28)},{v:-1.7}]},{c:[{v:new Date(2009,08,30)},{v:-1.1}]}]};
var data = new google.visualization.DataTable(object);
var annotatedtimeline = new google.visualization.AnnotatedTimeLine(
document.getElementById('visualization'));
annotatedtimeline.draw(data, {'displayAnnotations': true});
}
My guess is that you have something wrong when the numbers go around -1 and 1. Hope I helped you to track that issue