How's this for a horror story? With the usual harvest hustle, it's been too many days since a certain farmer downloaded the yield data he's been carefully collecting on his corn crop. So, before climbing off the combine late one night, he ejects the data card from the monitor and stuffs it (he thinks) into his shirt pocket, planning to download at home.

But between combine and pickup the card slips out, prompting a mini panic attack 30 minutes later when he reaches into his empty pocket. After cleaning out the pickup three times, he mentally retraces his steps to pinpoint where he must have dropped the card. Relaxing, he tells himself he'll just find it in the morning.

However, the next day an employee gets an early start disking stalks and - you guessed it - disks up the field, the card and the data.

This farm fable - told as a true story at the National Farm Machinery Show - illustrates one of the cardinal rules of using yield monitors: Download early and often.

That's only one hint equipment specialists offer for you to get the most from your monitor. Here are other pointers to consider, whether you're a veteran of harvesting bytes and bushels or if this is your rookie season behind a monitor.

Start by refreshing your memory about monitor operation. If you do not want to sit in the combine cab, pull the monitor and hook it to an AC adapter in your shop, office or kitchen. With the owner's manual open, push buttons, even if you're not setting up files for fields and grain types.

Getting comfortable with the monitor eliminates the frustration of trying to learn or relearn the system during harvest. And if you're frustrated, you'll give up and not collect the data, warns Andy Hill. He's a precision ag consultant from Auburn, IN, who sells, installs and troubleshoots monitors and GPS rigs for farmers in five states.

This exercise will also help spot electrical problems. "Mice have a taste for wiring harnesses," notes Chris Foster, senior marketing support specialist for Deere's Precision Farming.

The hardware and software manufacturers will probably notify you, but call them anyway about system upgrades that can make your life easier.

For example, Deere and Agco report changes for 1999. Deere's upgrade automatically calibrates the mass flow sensor's zero reading every three seconds. This is important to maintain accuracy when combining in changing temperatures or on hillsides.

Previously, you had to calibrate the zero reading manually. Agco's upgrade for its FieldStar yield map features several changes, but emphasizes the ability to export data to other software.

Check other elements besides the monitor. Make sure the distance between elevator paddles and the deflection shield is correct, for example. "This determines the accuracy across changing yields," says Hill.

And be sure the header-height sensor is set right and functioning properly. Look for bent rods or bad sensors.

"The header turns the monitor on and off, and if the unit isn't on it can't record. That causes about 50 of my initial calls," says Hill.

Also check the availability of the Coast Guard or satellite signal for your GPS antenna. It's an element that Jerry Schmitt, Agco's FieldStar general marketing manager, says is vital to getting the most from the data you collect. For subscription satellite services, make sure you're paid up.

Understand the monitor's accuracy and what you're really trying to measure.

"Yield monitors aren't out there to replace certified scales," Foster notes. "You need to use the data and maps to spot trends and variations in fields in order to make better production decisions. A lot of variables affect accuracy, but 95% accuracy or better is achievable."

Agco's Schmitt agrees. "You can have 95-99% accuracy depending on the crop. But yield monitors were designed to show changes within a field. If you want accuracy to within 0.1 bu/acre, you're missing the point of what a yield monitor is for."

Achieving and maintaining accuracy demands calibration every season.

"You don't want to rush through it. You'll live with the results throughout the season," Foster warns.

Pick an amount for calibration and stick with it, says Hill, who recommends 4,000-6,000 lbs. And consider calibrating to meet changes in a crop, such as different moisture levels. Some farmers calibrate for corn at three moisture levels, he reports.

Figure the correct header width when you calibrate.

"This is really simple, but it's really important. If you ignore this you may not understand why your bushels-per-acre is off," Hill says.

As for data, make sure you have enough clean cards and think download daily - even if you don't have to. Deere can stack 330 separator hours on an 8-megabyte card.

Agco's monitor tells you available space on the 2-meg cards, which usually hold 30 hours or about two days.