Beer smith mobile app question

Hi All
Just got the app. Had a question about the Batch Sparge Options
Batch Sparge: Yes
Use equal batches: No
Fill mash tun: 90.0 %
Drain tun before sparge: No

What do they mean by use equal batches. I thought that you use 1.5 times the amount of water when batch sparging.
Any help
Slainte

Use equal batches means that if you need to sparge more than once should the batches of sparge water be split perfectly in half. I usually have to sparge twice and mine are not split in half; I opt for about 2/3 on the first sparge and 1/3 on the second sparge.

You would technically use the amount of water needed to reach your preboil volume which will highly depend on your water:grist ratio.

stpug has it correct.

The fill % can also come into play as well. Here is how the two settings (use equal batches, and Fill %) interact...

Lets say you need 7 gallons of sparge water to hit your pre-boil volume, and your tun, with the grain already mashed, can only handle 6 gallons when filled to the very top

Fill to 90% means only fill the tun with 5.4 gallons (6 * 0.9) so you have a little head room.
With the "Use equal batches" set to NO, Beersmith will calculate one 5.4 gallon batch, and one 1.6 gallon batch to make up your 7 gallons.
With the "Use equal batches" set to YES, it will calculate 2 batches of 3.5 gallons each.

I have found that I need to use a bit of common sense when the setting is set to 'NO' because I have seen the software calculate a second batch size of less that a gallon, which was not practical on my system.