From my trial and error attempts it appears that the graph function is limited to 160 data points. Is that true? Can this be changed? If you try to extend X beyond 160 you will be getting only every several time steps available to enter a data value. Say if X=320 you'll get to enter only every second day of data. No way to enter all the 365 data points that I may have for, say, a year. Is that really so? Any way this can be changed? Is it documented anywhere?
Graph function X axis is limited to 160 points
That's right, the limit is 160 X axis points. The sketch graph is not really intended for the entry of accurate data sets. To do this you should really be using a file parameter. In your case it looks like you need a time series parameter -- see here