Varying minimum on charts w/o changing for each chart

Hi--

I make an xy scatterplot and then use the one graph to look at many
columns of data (I just move the blue box from column to column).
Each column has values that are fairly consistent, but the values vary
dramatically among the columns of numbers. For that reason, I need to
minimum value to vary.

Sometimes (magically), in a given graph, the minimum value on the y
axis shifts to reflect the data (eg numbers from 50-100, minimum of
45) as I shift among columns, but other times, on diffferent graphs on
different spreadsheets, the minimum is 0 when I set it as auto. What
I can't figure out is how to get the minimum value to vary with the
data consistently.

THanks in advance