Semi-log graph paper, A4
A logarithmic vertical axis against a linear horizontal one, on A4, the sheet that turns exponential growth into a straight line.
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What the log axis is actually doing
On a logarithmic axis, equal distances represent equal ratios rather than equal differences. The gap from 1 to 2 is the same physical distance as the gap from 10 to 20, or 100 to 200. This is why the divisions crowd together toward the top of each decade. They are not badly drawn, they are correct. Once that clicks, reading these sheets stops being awkward.
Exponential data plots straight
Anything of the form y = ab^x becomes a straight line on semi-log paper, and the slope of that line gives you the growth rate directly. Bacterial growth, radioactive decay, compound interest, capacitor discharge and unchecked epidemic spread all qualify. The practical value is diagnostic: if your data plots straight here, the underlying process is plausibly exponential, and if it curves, it is not, which is information you cannot get by eye from a linear plot.
Choosing the number of decades
Each decade is one factor of ten. Count the range your data actually spans, 5 to 4,000 spans three decades, and choose a sheet with at least that many, because you cannot extend a logarithmic axis by taping on another sheet the way you can a linear one. Too many decades and your data is squashed into a corner; too few and it runs off the page. If both axes need log scales, you want log-log paper instead, which straightens power laws rather than exponentials.
Printing it accurately
This only measures correctly if your printer doesn't rescale the page. In the print dialog set Scale: 100%, not "Fit to page" or "Shrink oversized pages". If you're not sure it worked, print the calibration page, measure the ruler on it with a real ruler, and it will tell you exactly what your printer is doing to the page.