Due to varying inherent capacitance and varying meter impedance from one meter to the next, making this adjustment using only a DVM on the DC scale is not a good idea IMHO.

You can buy a very good meter at Sears for less than $30 with a duty cycle scale. They have even been on sale for $19.95 at times.

You've heard the old adage, "use the right tool for the right job," this goes double for test equipment.

Good luck,