I have an older Sportline pedometer with the same three button arrangement.
My pedometer is set as follows:
First press Mode to get the unit in the Distance mode. Note if the unit is in Kilometers or Miles. (Press and hold Reset for 5 seconds to switch the setting. This will reset the entire pedometer.) Press and hold Set for 2 seconds. The current (or default) step length will appear and flash. Press Set repeatedly until your step length is displayed. It changes by 1" or 1 cm at a time. Then release the Set button. (The pedometer will return to the normal operating mode if you do not press a button for 5 seconds.) When you reach the maximum step length, the unit will advance to the lowest step lenght when you press Set again. Since my step length is actually not a whole number, I rounded down.
A different Sportline step and distance pedometer (the 340) is set slightly differently. To switch from Miles to Kilometers, press and hold Mode when in the Step mode. Then switch to the distance mode and press and hold Set until the step length flashes. Press Reset to advance the current step length by 1" or 2 cm. Then release the button when you have the correct step length displayed. The pedometer will return to the normal mode after 5 seconds with no button presses.
Many Sportline pedometer manuals are available from the company's web site on the product site: http://www.sportline.com
. You can look up the model number.
If you add your Sportline pedometer model, I'll be glad to give the specific setting procedure for you.
I hope this helps.
(on her third Sportline pedometer, two had the plastic spring clip fail. They all had similar programming details.)