For the last 3 days my weight averaged 75kgs. Using the same power recorded at the last 20 min power test, this predicts a 60 min PWR of 4.09, up from 4.03 at the weekend (obviously all due to the reduction in recorded weight!) which is a 1.5% improvement*.
*The reality is more likely to be that my recorded weight last weekend was too high as my activity and diet is unlikely to have resulted in a 0.9kg weight loss. Using the 3500kCals per lb guestimate of weight reduction, I'd have had to have used an additional 6900kCals to drop the weight, which I haven't, so such small changes are likely to be 'noise' and may have been caused by having a fuller stomach, being better hydrated or having a fuller bladder rather than any real weight loss. This is why I'm taking a longer-term view of the power and weight in my target.