According to this link, sugar heated to the lowest temperature in the Homebrewer's Association article (236°F) will result in a syrup with a 15% water content. The water content drops to 10% if the temperature gets around 250°F and drops to 1% if the temperature gets to 300°F.
As a sanity check, this article says that invert syrup gives 36 ppg (points per pound per gallon), whereas rock sugar gives 45 ppg, suggesting that there is 20% water content in the syrup.
So one pound of granulated sugar, heated to 236°F should yield 1.18 to 1.25 pounds of invert syrup and should be in the range of 36 to 39 ppg.
ADDITIONAL INFORMATION:
This answer is being appended, about a year later.
Summary
An experiment was performed with a 4 pound bag of table sugar. Water was not measured (no way to measure evaporation), but the weight of the crystal sugar and the resulting syrup were measured. The result was that the invert syrup provides 36 gravity points per pound per gallon. This is agreement with the link above.
Process
The "4 pound" bag of sugar contained 1803g net weight. After bringing water and sugar to 237 degrees F, I measured the weight of the finished product, plus the residue on the equipment and it came to 2331g. The total in the jars was 2314g and the volume was 1638ml, so the density of the syrup was 1.412g/ml.
Result
This experiment indicates that one pound of granulated sugar will yield 1.29 pounds of invert syrup if the syrup is heated to 237F. The resulting density will be about 1.41g/ml.
Because table sugar is 46 ppg, this would mean that the syrup made by this process would be 36 ppg.
