Backlash will be the sum of feed screw wear, feed screw nut wear, thrust bearing free play, and lead screw twist due to frictional drag in the ways. Excessively tight ways will increase backlash. To get a true indication, it would be best that the gib be loosened to the point where any drag is removed.
You can determine if the screw is worn by measuring backlash in the most used region and at the far end of travel. The far ends will have the least wear. Ideally, it will be the same or reasonably close.
A rough assessment of backlash can be achieved by rotating the crank in one direction enough to account for any backlash. Note the reading and slowly rotate in the opposite direction until some resistance is met. Note the difference in the reading.
A more accurate method would be to use a dial indicator or a test indicator. Set the indicator up to measure the cross slide travel. Rotate the crank to feed the cross slide into the indicator and note the indicator position and the cross feed dial reading. Continue moving past, then back until the indicator reads the the same position and note the cross feed dial reading. The difference is backlash.