Though equity will not permit the parol evidence rule to prevent it from granting relief for mistake, " the purpose of a written contract is to furnish a record of the terms of the agreement of the parties not easily impeached, and thereby to avoid subsequent disputes and conflicting testimony and claims regarding its terms and their meaning. To accomplish this purpose, and to prevent such disputes from annulling written agreements, two rules have been firmly established in equity: First, that the burden is on the complainant to prove the mutual mistake, or the mistake of .one party and the deceit, fraud, or inequitable conduct of the other, upon which he relies for a modification or avoidance of the contract; and, second, that in view of the written record of the terms of the agreement made at the time a preponderance of the evidence is insufficient, and nothing less than evidence that is plain and convincing beyond reasonable controversy will constitute such proof as will warrant a modification or reformation of a written agreement."76
Though it is settled that there must be more than a mere preponderance of evidence in order to justify relief in equity from mistake in a written instrument, the language of different courts varies in regard to the quantum of evidence necessary to sustain the burden of proof thrown upon one who seeks relief. In many cases it is said that proof must be beyond a reasonable doubt,77 but this mode of expression has been criticized,78 and the better and commoner way of appraising the quantum of proof is to state that the evidence must be clear and satisfactory or words of similar effect.79
677, 30 U. S. App. 40, 14 C. C. A. 60; Hurto v. Grant, 90 Iowa, 414, 57 N. W. 899; Yocum v. Foreman, 14 Bush, 494; jEtna Indemnity Co. v. Baltimore, etc., R. Co., 112 Md. 3S9, 76 Atl. 251, 136 Am. St. Rep. 389; Paulison v. Van Iderstine, 28 N. J. Eq. 306; White v. Campbell, 80 Va. 180; Sable v. Moloney, 48 Wis. 331, 4 N. W. 479; Van Brunt v. Ferguson, 163 Wis. 540, 158 N. W. 295. See also supra, Sec.1594.
76 Bailey v. Lisle Mfg. Co., 238 Fed. 257, 266, 152 C. C. A. 3.
77 Moore v. Tate, 114 Ala. 582, 21 So. 820; Parker v. Carter, 91 Ark. 162, 120 S. W. 836, 134 Am. St. Rep. 60; Franklin v. Jones, 22 Fla. 526; Houser v.
Austin, 2 Idaho, 204, 10 Pac. 37; Sutherland v. Sutherland, 69 HL 481; Wachendorf v. Lancaster, 61 Iowa, 509,
16 N. W. 533, 14 N. W. 316; Dare v. Foy, 180 la. 1156, 164 N. W. 179; Schaefer v. Mills, 69 Kans. 25, 76 Pac. 436; Andrews v. Andrews, 81 Me. 337,
17 Atl. 166; Stockbridge Iron Co. v. Hudson Iron Co., 102 Mass. 45, 107 Mass. 290; Steinberg v. Phoenix Insurance Co., 49 Mo. App. 255; Henderson v. Stokes, 42 N. J. Eq. 586, 8 Atl. 718; Boyertown Nat. Bank v. Hartman, 147 Pa. 558, 23 Atl. 842, 30 Am. St. Rep. 759; Deseret Nat. Bank v. Dinwoodey, 17 Utah, 43, 53 Pa. 215; Bailey v. Woodbury, 50 Vt. 166;