Depends on the machine, they are different & drag drops as they get full up with dust & crud.
On model Cs if you press 'REST' & OK' buttons simultaneously and then start rowing (at about 2:15 split) it will give a drag factor in the bottom right of the display. Increasing the damper setting (1 - 10) increases the drag factor. Somewhere between 125 & 150 will suit most people, but have a play and see what suits you best. With this you can set up any machine to have the same drag regardless of any foibles. Dunno about new fangled D, E & Dynamic models.
New ergo ladder in rowing club & intervention of British Rowing 'Start' programme coach has thrown up (unfortunate turn of phrase) new hard-as-you-can tests:
30 mins at 20spm (horrible)
250m at 40-44spm (barking).
You're welcome to have as much fun with those as can be wrung out...