The Beis HaVaad writes,
"Since no Divine name is used for a Shevuas Heses, the various tactics that instill fear mentioned earlier are not necessary, but Bais Din should nevertheless try to put pressure on the litigants to come to an agreement without resorting to an oath.
As is apparent from the above, making a false oath is a serious matter. For this reason, some Miforshim (Rashi, Rema) discontinued the use of a real Shevua in Bais Din, and substituted it instead with an Arur, or curse, in the presence of a Minyan. Since there are indications in the Gemara (Shevuos 39B) and Yerushalmi (Shevuos 6,5) that even a truthful oath is a cause of misfortune, the common practice in Betei Din is to offer the alternative of a Pshara, or compromise, instead of a Shevua. The accepted custom regarding this compromise is that the litigant who would normally have to swear forgoes a third of his claim, and thus frees himself of his obligation. The Divrei Malkiel (2, 133) and Igros Moshe (CH.M., 1, 32) add that this is merely the rule of thumb in the absence of any factor pointing to either side of the dispute, otherwise, wisdom should be used in order to determine the right terms for this compromise. R’Nissan Karelitz (quoted in Mishpetei Tzedek, P. 63) says that only when a Shevua Miderabbanan is in question is a third considered to be a sufficient deduction, but if one wishes to be absolved of a Shevua Mideoraisa, he must in turn relinquish half of his claim."