I think you may need to get a computer to plug into the ECMs to pull the hours off of them, unless the previous owner installed an aftermarket hour meter to quickly check hours. To read the actual hours, you need to either buy the computer or go to a dealer. If there is an aftermarket hour meter, it may not be the true operational hours, depending upon how it's wired. Some wire it directly to the accessory system so even though the engines may not be running, it may count that time as part of the hours. If the previous owner never uses the accessories without the engines off, pretty accurate. Depending upon which model or type is used, their accuracy of time may differ than the ECM just because how it interprets signals.